• Journal of Advanced Navigation Technology
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• v.20 no.5
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• pp.425-432
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• 2016

When user estimates user's position, GPS positions can be obtained from the navigation message transmitted from the GPS. However, the broadcast ephemeris cannot be used in the applications required high-level accuracies because it can cause errors of several meters. To correct satellite positions and clocks, user can use RTS corrections provided by IGS. In this paper, the accuracy of broadcast and RTS corrections are analyzed by comparing with the IGS final for 3-months. The RTS errors are analyzed for each user's locations and satellite blocks. The correlations between errors and shadow condition, and solar and geomagnetic activities are analyzed. The latency is applied to the RTS corrections, and these are extrapolated by polynomial. Then, the extrapolated RTS are compared with true RTS. The single-day performances of the PPP by broadcast ephemeris and RTS corrected ephemeris are analyzed. As a result, RTS 3D orbit and clock errors are 1/20 and 1/3 less than broadcast ephemeris errors. 3D positioning error of the RTS is 1/5 less than that of broadcast ephemeris.

• Asian Journal of Atmospheric Environment
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• v.10 no.4
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• pp.179-189
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• 2016

Here we evaluated the effect of using water retentive pavement or WRP made from fly ash as material for main street in a real city block. We coupled computational fluid dynamics and pavement transport (CFD-PT) model to examine energy balance in the building canopies and ground surface. Two cases of 24 h unsteady analysis were simulated: case 1 where asphalt was used as the pavement material of all ground surfaces and case 2 where WRP was used as main street material. We aim to (1) predict diurnal variation in air temperature, wind speed, ground surface temperature and water content; and (2) compare ground surface energy fluxes. Using the coupled CFD-PT model it was proven that WRP as pavement material for main street can cause a decrease in ground surface temperature. The most significant decrease occurred at 1200 JST when solar radiation was most intense, surface temperature decreased by $13.8^{\circ}C$. This surface temperature decrease also led to cooling of air temperature at 1.5 m above street surface. During this time, air temperature in case 2 decreased by $0.28^{\circ}C$. As the radiation weakens from 1600 JST to 2000 JST, evaporative cooling had also been minimal. Shadow effect, higher albedo and lower thermal conductivity of WRP also contributed to surface temperature decrease. The cooling of ground surface eventually led to air temperature decrease. The degree of air temperature decrease was proportional to the surface temperature decrease. In terms of energy balance, WRP caused a maximum increase in latent heat flux by up to $255W/m^2$ and a decrease in sensible heat flux by up to $465W/m^2$.

• KIISE Transactions on Computing Practices
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• v.21 no.1
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• pp.29-39
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• 2015

When new inertial navigation systems for an unmanned aerial vehicles are being developed and tested, construction of a fault-tolerant system is required because of various types of hazards caused by S/W and H/W faults. In this paper, a new fault-tolerant flight system that can be deployed into one or more FCCs (Flight Control Computers) is introduced, based on a partition scheme wherein each OFP (Operational Flight Program) partition uses an independent CPU and memory slot. The new fault-tolerant navigation system utilizes one or two FCCs, and executes a primary navigation OFP under development and a stable shadow OFP partition on each node. The fault-tolerant navigation system based on a single FCC can be used for UAVs with small payloads. For larger UAVs, an additional FCC with two OFP partitions can be used to provide both H/W and S/W fault-tolerance. The developed fault-tolerant navigation system significantly removes various hazards in testing new navigation S/Ws for UAVs.

• Journal of the Korea Society for Simulation
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• v.20 no.1
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• pp.107-116
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• 2011

Recently, femtocell has been concerned as one of effective solutions to relieve shadow region and provide high quality services to users in indoor environments. Even though femtocell offers various benefits to cellular operators and users, many technical issues, such as interference coordination, network synchronization, self-configuration, self-optimization, and so on, should be solved to deploy the femtocell in current network. In this paper, we develop a simulator for evaluating performance of long term evolution (LTE) femtocell systems under various interference scenarios. The simulator consists of a main-module and five sub-modules. The main-module connects and manages five sub-modules which have the functionality managing user mobility, packet scheduling, call admission control, traffic generation, and modulation and coding scheme (MCS). To provide user convenience, the simulator adopts graphical user interface (GUI) which can observes simulation results in real time. We expect that this simulator can contribute to developing effective femtocell systems by supporting a tool for analyzing the effect of interference between macrocell and femtocell.

• Journal of Information Display
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• v.4 no.3
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• pp.1-5
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• 2003

Laser-Induced Thermal Imaging (LITI) is a laser addressed patterning process and has unique advantages such as high-resolution patterning with over all position accuracy of the imaged stripes of within 2.5 micrometer and scalability to large-size mother glass. This accuracy is accomplished by real-time error correction and a high-resolution stage control system that includes laser interferometers. Here the new concept of hybrid system that complement the merits of small molecule and polymer to be used as an OLED; our system can realize easy processing of light emitting polymers and high luminance efficiency of small molecules. LITI process enables the stripes to be patlerned with excellent thickness uniformity and multi-stacking of various functional layers without having to use any type of fine metal shadow mask. In this study, we report a full-color hybrid OLED using the multi-layered structure consisting of small molecules and polymers.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.6B
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• pp.728-737
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• 2011

For the real time monitoring and tracking of shipping container which is one of the core objects for global logistics, Wireless Ad-Hoc Network technology might be needed in stacking environments such as ports, yards and ships. In this paper, we propose a container network routing protocol suitable for port or yard stacking environments which include some constraints such as shadow area problem from metal material, frequent movement of container, etc. With this protocol in which a mesh network algorithm is applied, every container data packet can be delivered to the sink node reliably even with frequent join/leave of container nodes. As soon as a node on path gets malfunction, alternative backup path is supported with notice to neighbor node, which makes constant total optimal path. We also verified that the performance of proposed protocol is better than AODV, one of previous major MANet(Mobile Ad-Hoc Network) protocol with a function for alternative path, which says the proposed protocol is better for frequent join/leave and variable link quality.

• Journal of Industrial Convergence
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• v.20 no.1
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• pp.63-68
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• 2022

In schools and corporate buildings, public WiFi Access Points are installed on the ceilings of hallways. In the case of an architectural structure in which a WiFi signal enters through a steel door made of a material with high signal attenuation, Internet connection is frequently cut off or fails when the door is closed. To solve this problem, our research implements an economical and portable WiFi extender using a Raspberry Pi and an auxiliary battery. Commercially available WiFi extenders have limitations in the location where the power plug is located, and WiFi extension using the WiFi hotspot function of an Android smartphone is possible only in some high-end models. However, because the proposed device can be installed at the position where the Wi-Fi reception signal is the best inside the door, the WiFi range can be extended while minimizing the possibility of damage to the original signal. Experimental results show that it is possible to eliminate the shadows of radio waves and to provide Internet services in the office when the door is closed, to the extent that web browsing and real-time video streaming for 720p are possible.

• Strategy21
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• s.39
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• pp.5-46
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• 2016

North Korea's 4th nuclear test on Jan. 6 and following developments once again awakened the world into seriousness of the nuclear matters on the Korean peninsula. On March 2, UNSC adopted Resolution 2270 which is complemented by Seoul government's measures such as withdrawal from the Gaesung Industrial Complex (Feb. 9) and announcement of unilateral sanction (March 8). Seoul government also strongly urged the international community to strangle North Korea's 'financial resources.' The U.S., Japan, China, and other countries have issued unilateral sanctions to complement the UNSC measure. South Korea and the U.S. conducted their annual joint military drill (Resolve-Foal Eagle) in the largest-ever scale. North Korea, however, responded with demonstration of its nuclear capabilities and announcement of de facto 'nuclear-first' politics. North Korea test-fired a variety of delivery vehicles, threatened nuclear strikes against South Korea and the U.S., and declared itself as an 'invincible nuclear power armed with hydrogen bombs' at the 7th Workers 'Party Congress held in May, 2016. Considering the circumstantial evidences, the North's 4th nuclear test may have been a successful boosted fission bomb test. North Korea, and, if allowed to go on with its nuclear programs, will become a nuclear power armed with more than 50 nuclear weapons including hydrogen bombs. The North is already conducting nuclear blackmail strategy towards South Korea, and must be developing 'nuclear use' strategies. Accordingly, the most pressing challenge for the international community is to bring the North to 'real dialogue for denuclearization through powerful and consistent sanctions. Of course, China's cooperation is the key to success. In this situation, South Korea has urgent challenges on diplomacy and security fronts. A diplomatic challenge is how to lead China, which had shown dual attitudes between 'pressure and connivance' towards the North's nuclear matters pursuant to its military relations with the U.S, to participate in the sanctions consistently. A military one is how to offset the 'nuclear shadow effects' engendered by the North's nuclear blackmail and prevent its purposeful and non-purposeful use of nuclear weapons. Though South Korea's Ministry of Defense is currently spending a large portion of defense finance on preemption (kill-chain) and missile defense, they pose 'high cost and low efficiency' problems. For a 'low cost and high efficiency' of deterrence, South Korea needs to switch to a 'retaliation-centered' deterrence strategy. Though South Korea's response to the North's nuclear threat can theoretically be boiled down into dialogue, sanction and deterrence, now is the time to concentrate on strong sanction and determined deterrence since they are an inevitable mandatory course to destroy the North' nuclear-first delusion and bring it to a 'real denuclearization dialogue.'

• Journal of the Society of Disaster Information
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• v.16 no.2
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• pp.402-410
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• 2020

Purpose: The purpose of this research is to eliminate communication shadowing loss of the 'smart safety management system'. The 'smart safety management system' can monitor and relay real time data of workers working in high risk workplace (i.e: industrial scene, disaster scene). The data will provide the rescue team the 'golden hour' in their rescue operations. Method: In this research, safety tag was designed and implemented so that it acts as a repeater for the user. Result: In other words, when communication in-between the safety tag and headquarters' communication terminal is jeopardized, the safety tag will act as a repeater-terminal for other safety tags in the area. Conclusion: The research tested if a specific building with communication shadowing loss problem was resolved when safety tags were implemented. Communication shadowing was first identified in-between the safety tag and headquarters' communication terminal. When extra safety tags were deployed in the same situation, the results showed that the communication shadowing loss was resolved. The repeater safety tags could resolve communication shadowing loss of up to three basement levels in this test building.

• Journal of the Korea Computer Industry Society
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• v.3 no.9
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• pp.1145-1156
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• 2002

A method to measure the speed and distance of moving object is proposed using the stereo vision system. One of the most important factors for measuring the speed and distance of moving object is the accuracy of object tracking. Accordingly, the background image algorithm is adopted to track the rapidly moving object and the local opening operator algorithm is used to remove the shadow and noise of object. The extraction efficiency of moving object is improved by using the adaptive threshold algorithm independent to variation of brightness. Since the left and right central points are compensated, the more exact speed and distance of object can be measured. Using the background image algorithm and local opening operator algorithm, the computational processes are reduced and it is possible to achieve the real-time processing of the speed and distance of moving object. The simulation results show that background image algorithm can track the moving object more rapidly than any other algorithm. The application of adaptive threshold algorithm improved the extraction efficiency of the target by reducing the candidate areas. Since the central point of the target is compensated by using the binocular parallax, the error of measurement for the speed and distance of moving object is reduced. The error rate of measurement for the distance from the stereo camera to moving object and for the speed of moving object are 2.68% and 3.32%, respectively.