• Journal of the Korea Society of Computer and Information
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• v.20 no.5
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• pp.1-12
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• 2015

NAND flash memory has being used for storage systems widely, because it has good features which are low-price, low-power and fast access speed. However, NAND flash memory has an in-place update problem, and therefore it needs FTL(flash translation layer) to run for applications based on hard disk storage. The FTL includes complex functions, such as address mapping, garbage collection, wear leveling and so on. Futhermore, implementation of the FTL on low-power embedded systems is difficult due to its memory requirements and operation overhead. Accordingly, many index data structures for NAND flash memory have being studied for the embedded systems. Overall performances of the index data structures are enhanced by a decreasing of page write counts, whereas it has increased page read counts, as a side effect. Therefore, we propose an index management method using a page mapping log table in $B^+$-Tree based on NAND flash memory to decrease page write counts and not to increase page read counts. The page mapping log table registers page address information of changed index node and then it is exploited when retrieving records. In our experiment, the proposed method reduces the page read counts about 61% at maximum and the page write counts about 31% at maximum, compared to the related studies of index data structures.

• Journal of rehabilitation welfare engineering & assistive technology
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• v.6 no.2
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• pp.15-22
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• 2012

The mechanical system of wearable walking assist robot needs to be optimized for adapting with human body structure and the planned control algorithm should have a secure procedure when a incongruity situation which can cause musculoskeletal injury occurs because a wearable robot is attached to a body. The understanding of walking or musculoskeletal motions characteristics must be preceeded and analyzed for developing novel wearable walking assist robot. In this study we tried to find out the capacities of powers and torques of joint actuators to design optimized performances of system and to obtain the analysis data to figure out the characteristics of joint movements during some types of walk. The major types of walk and motion are stair climbing and descending, sit-to-stand motion, and slope walking. In this study all these motions were analyzed experimentally except slope walking.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.435-435
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• 2012

ITER를 비롯한 실증로나 상용로급 토카막에서는 중성빔 가열이나 전류구동을 위해 1MeV이상의 빔 에너지가 요구된다. 빔 출력이 가속전압의 5/2승에 비례함에도 불구하고 양이온 빔의 경우 에너지가 높아지면 빔의 중성화 효율이 급격히 감소하여 ITER NBI의 경우 양이온 빔의 중성화 효율은 0%에 가깝다. 한편 음이온 빔은 1MeV 이상의 에너지영역에서도 빔 에너지와 거의 무관하게 60% 정도의 중성화 효율을 갖는다. 따라서 ITER는 음이온 빔을 바탕으로 한 중성빔 가열장치(N-NBI)를 채택하고 있다. 우리나라의 핵융합연구가 핵융합 발전을 지향하는한 N-NBI에 대한 연구를 시작해야 하며 그 출발점으로 음이온원 개념설계를 시작하였다. 개념설계는 음이온원 개발과정을 통해 1) 음이온 생성원리 규명, 2) 음 이온원 핵심기술 확보, 3) 음이온 및 음이온 빔 관련 진단 등을 연구할 수 있는 축소규모의 proto-type 음이온원 개발을 목표로 하였다. 음이온원 개발은, 초기에는 KAERI NB test stand 및 KAERI 이온원의 플라즈마 버켓을 활용하기 위해 filament-arc type으로 시작하지만 어느정도 기반이 확립되면 플라즈마 버켓의 electron dump를 제거하고 그 자리에 RF driver를 장착하여 궁극적으로 RF 음이온원을 개발할 계획이다. 본 학회에 발표하는 포스터는 filament-arc type 음이온원에 대한 개념설계이다. 설계된 음이온원은 Tent-type 자장필터를 장착하며, 0.5A의 수소 음이온빔 인출을 목표로 하고 있다. 이를 위해 플라즈마 버켓, 세슘 공급시스템, bias plate, 플라즈마 그리드, electron deflection 자석이 설치된 인출 그리드, 접지 그리드 등에 대한 개념설계가 이루어 졌다. 이 외에도 음이온원 전원과 진단 시스템에 대해서도 논의하였다.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.15 no.1
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• pp.253-259
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• 2015

In this paper, we propose a transformer of alternating voltage source utilizing a semiconductor, operating in bidirectional fashion. Transformer is a device transferring energy by inductive coupling between its winding circuits. Conventional transformer is a device, composed of a primary coil and a secondary coil, transforming an alternating voltage. The system we propose is designed with a single circuit transforming the level of voltage signal in two ways; from the source to the load, and vice versa. For semiconductor switches, the NPN transistor is connected to the alternating voltage source terminal, and emitter terminal is connected to the inductor in the system as an energy storage element. The control signal is applied to the base terminal of the semiconductors. We have shown that the system we propose, by adopting only one circuit, drives an alternating voltage transformer that changes the amplitudes of voltage signal in reciprocal way.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.6
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• pp.246-254
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• 2016

Thick-shell welding for super-sized oil storage tanks is currently done manually, which causes deterioration in quality and a lack of uniformity due to frequent rewelding. The limitations of the external environment must also be considered for manual welding. This paper describes the development of a carriage system for automatic vertical welding to increase reliability, reduce cost, and enhance productivity. The system consists of a welding platform, carriage device, and control unit, which were conceptually designed according to design specifications and manufactured with modular parts. In addition, the structure was analyzed for safety and to predict design problems in advance, and the results are reflected in reviewing the design. To evaluate the performance of the system, a tensile test, bending test, and weld time test were carried out, and the results were satisfactory. The time required for automatic weld was greatly improved by more than 87%, compared to the manual welding time.

• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.3
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• pp.294-302
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• 2004

In this study, we developed the inverter system to control Induction motor for the vertically circulation parking facility. In the case of calling a pallet, a car parking space, we basically stoned conventional system's problems, pallet is uncontrollable to the fixed position and braking system was worn by forcer braking with remaining speed. Also, by appling to converter controller, added to power regenerative control function, we confirmed the reduce of power supply capacity and the energy saving effect according to increasing operation frequency. The validity of this system is verified by 55kw induction motor driving system. Via this study, the proposed system shows the efficient use of parking facility and good operation characteristics by implementing position and speed control effectively on condition of load and shows energy saying effect by power factor control for the vertically circulation parking facility operation.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.43 no.3 s.309
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• pp.51-59
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• 2006

In this paper, we propose an excellent ultrasonic transceiver system based on a QPSK modulation technique for underwater communication. The transmitter sends a still image at the level of 187dB re $1{\mu}Pa/V@1m$ through a power amplifier by driving an ultrasonic sensor. The receiver performs digital conversion at the 100kHz sampling frequency, demodulation and decoding process for the image sent from the transmitter through the underwater communication. We have shown that the processed image at the receiver is almost the same as the orignal one. The maximum detection distance of the system proposed in this paper is approximately 1.17km. To cope with the difficulties of transmission loss, this paper proposes, implements and analyzes important parameters of sensors and circuits used in the system. Most of the underwater communication has focused on the transmission of audio signal, but this paper suggests an efficient underwater communication system for still image transmission.

• Progress in Superconductivity
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• v.13 no.2
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• pp.105-110
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• 2011

SQUID sensor-based ultra low-field magnetic resonance apparatus with ${\mu}T$-level measurement field requires a strong prepolarization magnetic field ($B_p$) to magnetize its sample and obtain magnetic resonance signal with a high signal-to-noise ratio. This $B_p$ needs to be ramped down very quickly so that it does not interfere with signal acquisition which must take place before the sample magnetization relaxes off. A MOSFET switch-based $B_p$ coil driver has current ramp-down time ($t_{rd}$) that increases with $B_p$ current, which makes it unsuitable for driving high-field $B_p$ coil made of superconducting material. An energy cycling-type current driver has been developed for such a coil. This driver contains a storage capacitor inside a switch in IGBT-diode bridge configuration, which can manipulate how the capacitor is connected between the $B_p$ coil and its current source. The implemented circuit with 1.2 kV-tolerant devices was capable of driving 32 A current into a thick copper-wire solenoid $B_p$ coil with a 182 mm inner diameter, 0.23 H inductance, and 5.4 mT/A magnetic field-to-current ratio. The measured trd was 7.6 ms with a 160 ${\mu}F$ storage capacitor. trd was dependent only on the inductance of the coil and the capacitance of the driver capacitor. This driver is scalable to significantly higher current of superconducting $B_p$ coils without the $t_{rd}$ becoming unacceptably long with higher $B_p$ current.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.6
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• pp.489-495
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• 2007

An experimental study was carried out in order to measure the pitch dynamic stability derivatives of a standard dynamics model in a low-speed wind tunnel. When a trigger signal is generated, the aircraft model starts oscillation with constant amplitudes and frequencies provided by DC electrical servomotor. The measured data are simultaneously recorded on a data recorder for 25 cycles of the model oscillation. The Phase shift needed to compute the dynamic stability derivatives is determined by calculating differences between the peak values of the input and output signals from the dynamic stability balance. Stabilator effects on the stability derivatives were also investigated with deflection angles. Although the driving apparatus and experimental equipments manufactured creatively for this study are different from other experiments, the variational trend of dynamic stability derivatives with the angle of attack is in a good accordance with the results of TPI, NAE, and FFA.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.12
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• pp.1115-1120
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• 2007

This paper presents a novel mechanism of electro-spray micro-thruster featured by a nozzle with a conductive pole inside, referred to here as a pole type nozzle. And the effects of the pole type nozzle on the efficiency of the jetting are numerically and experimentally investigated. The electric voltage signal applied to the upper electrode plate, against the pole as the ground, allows a ejection of spray to take place. It is verified experimentally that the use of the pole type nozzle allows a stable and sustainable jetting mode of ejection for a wider range of applied voltages because it can concentrate the electric field more on the centre of the meniscus. According to results about size effect, experiments indicates that the proposed mechanism allows that operation of micro thruster at less than 500 volts through nanoscale nozzle.