• The KIPS Transactions:PartA
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• v.16A no.5
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• pp.357-368
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• 2009

Mobile IP storage has been proposed to overcome storage limitation in the flash memory and hard disks. It provides almost capacity-free space for mobile devices over wireless IP networks. However, battery lifetime of the mobile devices is reduced rapidly because of power consumption with continuous use of a WLAN device when multimedia contents are being streamed through the mobile IP storage. This paper proposes an energy-efficient WLAN device power control technique for streaming multimedia contents with the mobile IP storage. The proposed technique consists of a prefetch buffer input/output module, a WLAN device power control module, and a reconfigurable prefetch buffer module. Besides, it adaptively determines the size of the prefetch buffer according to a quality of the multimedia contents, and it dynamically controls the power mode of the WLAN device on the basis of power on-off operations while streaming the multimedia contents. We evaluate the performance of the proposed technique on a PXA270-based mobile device that employs the embedded linux 2.6.11, Intel iSCSI reference codes, and a WLAN device. Extensive experiments reveal that the proposed technique can save the energy consumption of the WLAN device up to 8.5 times with QVGA multimedia contents, as compared with no power control.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.4
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• pp.527-535
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• 2017

Heat management is one of the most critical issues in Polymer Electrolyte Membrane Fuel Cells (PEMFCs) installed inside the fuel cell power pack of a fuel cell battery hybrid UPS. If the heat generated by the chemical reaction in the fuel cell is not rapidly removed, the durability and performance of the fuel cell may be affected, which may shorten its lifetime. Therefore, the objective of this study is to select and propose a proper cooling method for the fuel cells used in the fuel cell power pack of a UPS. In order to find the most appropriate cooling method, the various design factors affecting the cooling performance were studied. The numerical analysis was performed by a commercial program, i.e., COMSOL Multiphysics. Firstly, the surface temperature of the 1 kW class fuel cell stack with the cooling fans placed at the top was compared with the one with the cooling fans placed at the bottom. Various rotation speeds of the cooling fan, viz. 2,500, 3,000, 3,500, and 4,000 RPM, were tested to determine the proper cooling fan speed. In addition, the influence of the inhaled air flow rate was investigated by changing the porous area of the grille, which is the entrance of the air flowing from the outside to the inside of the power pack. As a result, it was found that for the operating conditions of the 1 kW class PEMFC to be acceptable, the cooling fan was required to have a minimum rotating speed of 3500 RPM to maintain the fuel cell surface temperature within an acceptable range. The results of this study can be effectively applied to the development of thermal management technology for the fuel cells inside the fuel cell power pack of a UPS.

• Journal of KIISE:Information Networking
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• v.36 no.4
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• pp.339-350
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• 2009

In wireless sensor networks, the limited battery resources of sensor nodes have a direct impact on network lifetime. To reduce unnecessary power consumption, it is often the case that only a minimum number of sensor nodes operate in active mode while the others are kept in sleep mode. In such a case, however, the network service can be easily unreliable if any active node is unable to perform its sensing or communication function because of an unexpected failure. Thus, for achieving reliable sensing, it is important to maintain the sensing level even when some sensor nodes fail. In this paper, we propose a new fault-tolerance scheme, called FCP(Fault-tolerant Coverage Preserving), that gives an efficient way to handle the degradation of the sensing level caused by sensor node failures. In the proposed FCP scheme, a set of backup nodes are pre-designated for each active node to be used to replace the active node in case of its failure. Experimental results show that the FCP scheme provides enhanced performance with reduced overhead in terms of sensing coverage preserving, the number of backup nodes and the amount of control messages. On the average, the percentage of coverage preserving is improved by 87.2% while the additional number of backup nodes and the additional amount of control messages are reduced by 57.6% and 99.5%, respectively, compared with previous fault-tolerance schemes.

• Journal of the HCI Society of Korea
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• v.14 no.2
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• pp.41-47
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• 2019

In this study, a smart assistive device is designed to recognize pedestrian signal and to provide audio instructions for visually impaired people in crossing streets safely. Walking alone is one of the biggest challenges to the visually impaired and it deteriorates their life quality. The proposed device has a camera attached on a pair of glasses which can detect traffic lights, recognize pedestrian signals in real-time using a machine learning algorithm on GPU board and provide audio instructions to the user. For the portability, the dimension of the device is designed to be compact and light but with sufficient battery life. The embedded processor of device is wired to the small camera which is attached on a pair of glasses. Also, on inner part of the leg of the glasses, a bone-conduction speaker is installed which can give audio instructions without blocking external sounds for safety reason. The performance of the proposed device was validated with experiments and it showed 87.0% recall and 100% precision for detecting pedestrian green light, and 94.4% recall and 97.1% precision for detecting pedestrian red light.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.22 no.1
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• pp.43-56
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• 2012

Wireless sensor networks consist of numerous small-sized nodes equipped with limited computing power and storage as well as energy-limited disposable batteries. In this networks, nodes are deployed in a large given area and communicate with each other in short distances via wireless links. For energy efficient networks, dynamic clustering protocol is an effective technique to achieve prolonged network lifetime, scalability, and load balancing which are known as important requirements. this technique has a characteristic that sensing data which gathered by many nodes are aggregated by cluster head node. In the case of cluster head node is exposed by attacker, there is no guarantee of safe and stable network. Therefore, for secure communications in such a sensor network, it is important to be able to encrypt the messages transmitted by sensor nodes. Especially, cluster based sensor networks that are designed for energy efficient, strongly recommended suitable key management and authentication methods to guarantee optimal stability. To achieve secured network, we propose a key management scheme which is appropriate for hierarchical sensor networks. Proposed scheme is based on polynomial key pool pre-distribution scheme, and sustain a stable network through key authentication process.

• Journal of Space Technology and Applications
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• v.3 no.2
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• pp.101-117
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• 2023

Active debris removal, a technology that approaches and removes space debris in orbit, and the on-orbit service, a technology for extending the mission life of satellites by fuel charging or by exchanging the battery, are gaining interest with the growth of the space community. SaTReC plans to develop a satellite capable of capturing and removing Korean satellites orbiting in space after the end of their missions. In contrast to the previously launched satellites by Korea, which were mainly intended to observe Earth and the space environment, rendezvous/docking technologies, as required in the future during, for instance, space exploration missions, will be implemented and demonstrated. In this paper, an orbital transition method for next-generation small satellites that will capture and remove space debris will be introduced. It is assumed that a small satellite with a mass of approximately 200 kg will be injected into the mission orbit through Korea Space Launch Vehicle-II in 2027. Because the satellite must access the target using a minimum amount of fuel, an approaching technology using Earth's J2 perturbation force has been developed. This method is expected to enable space debris removal missions for relatively lightweight satellites and to serve as the basis for carrying out a new type of space exploration in what is termed the 'Newspace' era.

• Journal of the Korean Electrochemical Society
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• v.26 no.1
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• pp.1-10
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• 2023

The cathode, which is one of the four major components of a lithium secondary battery, is an important component responsible for the energy density of the battery. The mixing process of active material, conductive material, and polymer binder is very essential in the commonly used wet manufacturing process of the cathode. However, in the case of mixing conditions of the cathode, since there is no systematic method, in most cases, differences in performance occur depending on the manufacturer. Therefore, LiMn₂O₄ (LMO) cathodes were prepared using a commonly used THINKY mixer and homogenizer to optimize the mixing method in the cathode slurry preparation step, and their characteristics were compared. Each mixing condition was performed at 2000 RPM and 7 min, and to determine only the difference in the mixing method during the manufacture of the cathode other experiment conditions (mixing time, material input order, etc.) were kept constant. Among the manufactured THINKY mixer LMO (TLMO) and homogenizer LMO (HLMO), HLMO has more uniform particle dispersion than TLMO, and thus shows higher adhesive strength. Also, the result of the electrochemical evaluation reveals that HLMO cathode showed improved performance with a more stable life cycle compared to TLMO. The initial discharge capacity retention rate of HLMO at 69 cycles was 88%, which is about 4.4 times higher than that of TLMO, and in the case of rate capability, HLMO exhibited a better capacity retention even at high C-rates of 10, 15, and 20 C and the capacity recovery at 1 C was higher than that of TLMO. It's postulated that the use of a homogenizer improves the characteristics of the slurry containing the active material, the conductive material, and the polymer binder creating an electrically conductive network formed by uniformly dispersing the conductive material suppressing its strong electrostatic properties thus avoiding aggregation. As a result, surface contact between the active material and the conductive material increases, electrons move more smoothly, changes in lattice volume during charging and discharging are more reversible and contact resistance between the active material and the conductive material is suppressed.

• Journal of IKEEE
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• v.23 no.4
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• pp.1461-1464
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• 2019

In this paper, we propose the development of embedded board for integrated radiation exposure protection fireman's life-saving alarm capable of location tracking and radiation measurement. The proposed techniques consist of signal processing unit, communication unit, power unit, main control unit. Signal processing units apply shielding design, noise reduction technology and electromagnetic wave subtraction technology. The communication unit is designed to communicate using the wifi method. In the main control unit, power consumption is reduced to a minimum, and a high performance system is formed through small, high density and low heat generation. The proposed techniques are equipment operated by exposure to poor conditions, such as disaster and fire sites, so they are designed and manufactured for external appearance considering waterproof and thermal endurance. The proposed techniques were tested by an authorized testing agency to determine the effectiveness of embedded board. The waterproof grade has achieved the IP67 rating, which can maintain stable performance even when flooded with water at the disaster site due to the nature of the fireman's equipment. The operating temperature was measured in the range of -10℃ to 50℃ to cope with a wide range of environmental changes at the disaster site. The battery life was measured to be available 144 hours after a single charge to cope with emergency disasters such as a collapse accident. The maximum communication distance, including the PCB, was measured to operate at 54.2 meters, a range wider than the existing 50 meters, at a straight line with the command-and-control vehicle in the event of a disaster. Therefore, the effectiveness of embedded board for embedded board for integrated radiation exposure protection fireman's life-saving alarm has been demonstrated.

• Progress in Medical Physics
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• v.19 no.2
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• pp.125-130
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• 2008

The object of this study is to measure the transit time and passage rate of capsule endoscopy (CE) in the gastrointestinal tract in medium sized beagle dogs ($7{\sim}13\;kg$). Animals were divided into four groups: only capsule (group 1, n=10), capsule+water (group 2, n=10), mettoclopramide+capsule (group 3, n=10), metoclopramide +capsule+water (group 4, n=10). The capsule transit times through the stomach and small bowel were evaluated by radiography findings. Gastric transit time (GTT), small intestinal transit time (SITT) and complete passage rate were measured in four groups. GTT's for each group were as follows; $45{\pm}20\;min$ (group 1), $117{\pm}35\;min$ (group 2), $150{\pm}40\;min$ (group 3), and $154{\pm}65\;min$ (group 4), while SITT's were $75{\pm}20\;min$ (group 1), $195{\pm}55\;min$ (group 2), $70{\pm}15\;min$ (group 3), and $76{\pm}15\;min$ (group 4). The complete passage rates were 20% (group 1), 40% (group 2), 20% (group 3), 50% (group 4). In all groups, if CE could pass through the pylorus, it passed all small intestinal tracts within 8 hours (battery life). Administration of water helped CE to pass pylori, except in case of metoclopramide administration. These results indicate that CE could be an useful tool for examining gastrointestinal diseases in the veterinary medicine.