• Journal of Navigation and Port Research
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• v.35 no.7
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• pp.557-562
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• 2011

Shipwaves can have harmful effects on people who are using riverside and cause bank erosion, bank structures destruction in restricted waterways. The wave field near a vessel is consisted of a combination of a primary and secondary wave system in a shallow or restricted waterway. The water level depression(squat) and return current beside the hull are called the primary wave system. The secondary wave system, that is the wave height originates from a local disturbance point such as the bow of the ship. This study aims at investigating the characteristics of the wave field around a vessel in a restricted water in relation to navigation experimentally and theoretically. The return current and squat with a correction factor can be newly evaluated and the almost same high-sized wave heights take place on the whole waterway in a restricted water without regard to the distance from the sailing line.

• International Journal of Aeronautical and Space Sciences
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• v.5 no.2
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• pp.43-53
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• 2004

Collision avoidance for multiple aircraft can be stated as a problem ofmaintaining safe distance between aircraft in conflict. Optimal collision avoidanceproblem seeks to minimize the given cost function while simultaneously satisfyingconstraints. The cost function could be a function of time or control input. This paper addresses the trajectory time-optimization problem for collision avoidance of unmanned aerial vehicles(UAVs). The problem is difficult to handle in general due to the two-point boundary value problem subject to dynamic environments. Some simplifying aleorithms are used for potential applications in on-line operation.Although under possibility of more complicated problems, a dynamic problem is transformed into a static one by prediction of the conflict time and some appropriate assumptions.

• Journal of Korea Spatial Information System Society
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• v.10 no.4
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• pp.21-26
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• 2008

A method for processing huge airborne laser scanned data using parallel computing and virtual grid is proposed and the method is tested by generating raster DSM(Digital Surface Model) with IDW(Inverse Distance Weighting). Parallelism is involved for fast interpolation of huge point data and virtual grid is adopted for enhancing searching efficiency of irregularly distributed point data. Processing time was checked for the method using cluster constituted of one master node and six slave nodes, resulting in efficiency near to 1 and load scalability property. Also large data which cannot be processed with a sole system was processed with cluster system.

• Journal of the Korean Society of Tobacco Science
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• v.25 no.1
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• pp.53-58
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• 2003

This study deals with the leaf tobacco assignment problem of a leaf tobacco warehouse with multiple input points and single output point. Also, the number of storage frequences is not necessary the same as that of retrieval for each leaf tobacco. A mathematical model is developed with the objective of minimizing the total travel distance associated with storage and retrieval operations. We also develop several heuristics based on the retrieval order frequency, retrieval/storage frequency ratio of leaf tobacco, and ABC curve. It is observed that the ABC curve based heuristic gives the best solution which is near optimal. Based on the test results from real world data, the ABC curve based heuristic is found to give a best performance. Comparing to current assignment method, the ABC curve based heuristic reduced total travel distance about 17.2%.

• Nuclear Engineering and Technology
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• v.53 no.5
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• pp.1587-1592
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• 2021

The effects of the symmetrical tilt Σ5 (310) <001> grain boundary (GB) on the evolution of radiation-induced point defects in pure δ-plutonium (Pu) were studied by Molecular dynamics (MD) simulations. The evolution of radiation-induced point defects was obtained when primary knock-on atom (PKA) was respectively set as -15 Å and 15 Å far from the GB and the number of residual defects was obtained as the distance from PKA to GB was changed. According to the results, compared with vacancies, interstitial atoms were more easily absorbed by GB. In addition, the formation energy of point defects was also calculated. The results showed that there was almost no difference for the formation energy of vacancies in the all matrix. However, the formation energy of interstitial atoms close to the GB was lower than that in the other bulk regions.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.3
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• pp.190-196
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• 1999

Continuation power flow has been developed to remove the ill-condition problem caused by singularity of power flow Jacobian at and near at steady-state voltage instability point in conventional power flow. Continuation power flow consists of predictor and corrector. In prddictor, the direction vector at the resent solution is caluculated and the initial guess of next solution is determined at the distance of step length. The selection of step length is a very important part, since computational speed and convergence performance are both greatly affected by the choice of the step length. This paper presents the practical step length selection algorithm using the reactive power generation sensitivith. In numulation, the proposed algorithm is compared with step length selection algorithm using TVI(tangent vector index).

• ETRI Journal
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• v.43 no.4
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• pp.580-593
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• 2021

When operating in confined spaces or near obstacles, collision-free path planning is an essential requirement for autonomous exploration in unknown environments. This study presents an autonomous exploration technique using a carefully designed collision-free local planner. Using LiDAR range measurements, a local end-point selection method is designed, and the path is generated from the current position to the selected end-point. The generated path showed the consistent collision-free path in real-time by adopting the Euclidean signed distance field-based grid-search method. The results consistently demonstrated the safety and reliability of the proposed path-planning method. Real-world experiments are conducted in three different mines, demonstrating successful autonomous exploration flights in environment with various structural conditions. The results showed the high capability of the proposed flight autonomy framework for lightweight aerial robot systems. In addition, our drone performed an autonomous mission in the tunnel circuit competition (Phase 1) of the DARPA Subterranean Challenge.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.2
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• pp.104-117
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• 1991

When a body starts to move, the flow near the intersection point between a body and a free surface changes violently and rapidly in a very short initial time interval. This flow phenomena must be investigated whenever one treats the interaction between a body and a fluid, such as the motion of a floating body, sloshing in a tank, wave maker problem, entry of a body into a fluid etc.. Until Roberts(1987), it was widely accepted that a singularity exists at the intersection point. However, he showed that the singularity does not exist if a body moves non-impulsively. In this paper, an analytical solution cosistent for the case of impulsive motion of a body is obtained by including the effect of surface tension. From the characteristics of the newly obtained solution, a critical value associated with an oscillating phenomenon is found, and further more, it is shown that the oscillating phenomenon does not appear in the region where the distance form the intersection point is less than this critical value.

• Journal of The Korean Astronomical Society
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• v.37 no.4
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• pp.285-288
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• 2004

Near-infrared imaging photometry supplemented by optical spectroscopy and narrow-band imaging of the H II region Sh 2-128 and its environment are presented. This region contains a developed H II region and the neighboring compact H II region S 128N associated with a pair of water maser sources. Midway between these, the core of a CO cloud is located. The principal ionizing source of Sh 2-128 is an 07 star close to its center. A new spectroscopic distance of 9.4 kpc is derived, very similar to the kinematic distance to the nebula. This implies a galactocentric distance of 13.5 kpc and z = 550 pc. The region is optically thin with abundances close to those predicted by galactocentric gradients. The $JHK_s$ images show that S 128N contains several infrared point sources and nebular emission knots with large near-infrared excesses. One of the three red Ks knots coincides with the compact H II region. A few of the infrared-excess objects are close to known mid- and far-infrared emission peaks. Star counts in J and $K_s$ show the presence of a small cluster of B-type stars, mainly associated with S 128N. The $JHK_s$ photometric properties together with the characteristics of the other objects in the vicinity suggest that Sh 2-128 and S 128N constitute a single complex formed from the same molecular cloud, with ages ${\~}10^6$ and < $3 {\times} 10^5$ years respectively. No molecular hydrogen emission was detected at 2.12 ${\mu}m$. The origin of this remote star forming region is an open problem.

• Annals of Clinical Neurophysiology
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• v.19 no.1
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• pp.28-33
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• 2017

Background: Previous studies of radial nerve conduction study (NCS) did not present how to measure the length of the radial nerve across the elbow, and did not even mention how to manage the spiral course of the nerve. This study aimed to applicate the most reliable method to measure the length of the radial nerve during NCS. Methods: Three points (A, B, and C) were determined along the relatively straight course of the radial nerve. The distance was measured using three different methods: L1) straight distance corresponding to the A-C distance, L2) sum of the distances corresponding to the A-B-C distance, L3) based on the L2, but the elbow is flexed at a $45^{\circ}$ angle. We compared the three methods of distance measurement and the calculated nerve conduction velocities (V1, V2, and V3) in normal healthy subjects. Results: 19 normal participants were enrolled. The mean value for method L1, L2 and L3 were $22.5{\pm}1.8cm$, $24.0{\pm}2.1cm$, and $23.2{\pm}2.1cm$ (p < 0.001). Calculated conduction velocities using those distance measurement methods as follows (p < 0.001): V1 ($60.9{\pm}2.7m/s$), V2 ($64.6{\pm}3.3m/s$), and V3 ($63.4{\pm}3.9m/s$). V2 was significantly greater than V1 and V3 (p < 0.001, p = 0.010, respectively). Conclusions: The distance measurement using a stopover point near the lateral epicondyle between two stimulus points in position of a fully extended elbow with forearm pronation is the most appropriate posture for radial motor NCS.