• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.12 no.3
• /
• pp.378-390
• /
• 2001

In this paper, it is analyzed that the error performance of a Multi-Carrier DS-CDMA system in a single cell with multipath Rician fading and multiple access interference (MAI) and the error performance of the system is compared with that of a Sing1e-Carrier DS-CDMA system. Moreover, the convolutional coding techniques with code rate of 1/2, 1/3, and 1/4 are adopted in order to improve the error performance degraded by the multipath fading and MAI and performance improvement through the coding techniques is analyzed. As a result, it is shown that the number of users in each system can be determined by the number of branches of the rake receiver in a Single-Carrier DS-CDMA system and the number of carriers in a Multi-Carrier DS-CDMA system. Furthermore, the convolutional coding should be chosen with considering the trade-off between coding gain and a power limitation in a Multi-Carrier DS-CDMA system. In case of increasing the number of carriers, the processing gain is decreased but the error performance is improved through the effect of frequency diversity and the system can be possibility implemented due to the low chip rate.

• Journal of electromagnetic engineering and science
• /
• v.13 no.2
• /
• pp.113-119
• /
• 2013

We developed a transformed, symmetrical, mushroom-like surface without via holes in cells focused on a 2.4-GHz WLAN band. Each slot in the novel type structure plays a key role in modeling at the desired frequencies. The designed artificial magnetic conductor (AMC) has several advantages, including a small size, a wider bandwidth, a short reflecting distance to the antenna, and easy fabrication because there are no via holes. Overall dimensions of the AMC cell are 21 mm $(Width){\times}21mm$ $(Height){\times}2.6mm$ (Thickness), and the bandwidth is about three times wider (11.7%) compared to that of a conventional AMC (4.0%). For evaluating the performance of the proposed structure, a reflector, which periodically consists of the designed AMC cells, was developed. The antenna with the investigated AMC reflector not only works within a quarter of the wavelength because of the extremely high wave impedance generated by the AMC cells on the surface of the structure but also reduces the specific absorption rate (SAR). Electromagnetic field (EMF) exposure to a human phantom was analyzed by applying the designed reflector to the 2.4-GHz dipole antenna in a tablet PC. The calculated peak SAR averaged over 1 g was 0.125 W/kg when the input power was 1 W and the antenna was located at 20 cm from the human phantom. However, the SAR value was only 0.002 W/kg (i.e., 98.4% blocked) when the designed reflector was inserted in front of the antenna.

• Journal of Hydrogen and New Energy
• /
• v.21 no.3
• /
• pp.227-240
• /
• 2010

Coal gasification is heading for a great future as one of the cleanest energy sources, which can produce not only electricity and heat, but also gaseous and liquid fuels from the synthesis. The work focuses on 300MW shell type one-stage entrained flow coal gasifier which is used in the Integrated coal Gasification Combined Cycle(IGCC) plant as a reactor. As constructing an IGCC plant is considerably complicated and expensive compared with a pulverized-coal power plant, it is important to determine optimum design factors and operating conditions using a computational fluid dynamics (CFD) model. In this study, the results of numerical calculations show that $O_2$/Coal ratio, 0.83, Steam/Coal ratio, 0.05, coal particle diameter, $100{\mu}m$, injection angle, $4^{\circ}$ (clockwise) are the most optimum in this research.

• Journal of Hydrogen and New Energy
• /
• v.29 no.3
• /
• pp.251-259
• /
• 2018

Metal hydride based hydrogen storage under moderate temperature and pressure gives the safety advantage over the gas and liquid storage methods. Still solid-state hydrogen storage including metal hydride is below the DOE target level for automotive applications, but it can be adapted to stationary or miliary application reasonably. In order to develop a modular solid state hydrogen storage system that can be applied to a distributed power supply system composed of renewable energy - water electrolysis - fuel cell, the heat transfer and hydrogen storage characteristics of the metal hydride necessary for the module system design were investigated using AB5 type metal hydride, LCN2 ($La_{0.9}Ce_{0.1}Ni_5$). The planetary high energy mill (PHEM) treatment of LCN2 confirmed the initial hydrogen storage activation and hydrogen storage capacity through surface modification of LCN2 material. Expanded natural graphite (ENG) addition to LCN2, and compression molding at 500 atm improved the thermal conductivity of the solid hydrogen storage material.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2002.05a
• /
• pp.257-260
• /
• 2002

This paper describes a design of cryptographic processor that implements the AES (Advanced Encryption Standard) block cipher algorithm“Rijndael”. To achieve high throughput rate, a sub-pipeline stage is inserted into the round transformation block, resulting that the second half of current round function and the first half of next round function are being simultaneously operated. For area-efficient and low-power implementation the round transformation block is designed to share the hardware resources in encryption and decryption. An efficient scheme for on-the-fly key scheduling, which supports the three master-key lengths of 128-b/192-b/256-b, is devised to generate round keys in the first sub-pipeline stage of each round processing. The cryptoprocessor designed in Verilog-HDL was verified using Xilinx FPGA board and test system. The core synthesized using 0.35-${\mu}{\textrm}{m}$ CMOS cell library consists of about 25,000 gates. Simulation results show that it has a throughput of about 520-Mbits/sec with 220-MHz clock frequency at 2.5-V supply.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2002.11a
• /
• pp.151-155
• /
• 2002

In this paper, interference effects between NGSO and HAPS analyze into two cases. One is HAPS interference effect into NGSO, another is NGSO interference effect into HAPS. First, same case of number of users for LEO and HAPS interference received to LEO mobile station are over the -8.82dB. But in case of 1/10 and 1/100, I/N values are lowest 16.9dB and -20.3dB respectively. In case of interference received to HPAS mobile station, as LEO is 87$^{\circ}$, if the HAPS and LEO users is same, interference criterion over the 2200 users. but in the case of 1/10 and 1/100 of LEO is HAPS users, we don't know over the interference criterion. In accordance with, for reduce to effects of interference important suitable establishment of transmission power, number of users and cell radius of two system.

• Proceedings of the KIPE Conference
• /
• 2018.07a
• /
• pp.72-74
• /
• 2018

기존 자동차 및 트럭용 Jump Starter의 경우, 일반적인 자동차용 납축전지를 이용하여 사용하기 때문에 부피와 무게가 매우 커 휴대성이 어렵고, 고가의 제품군으로 형성되어 있어 일반 운전자들은 구입 및 사용하기 어려운 문제가 있다. 또한 리튬배터리를 이용한 Jump Starter의 경우, 부피는 줄었지만 원가가 매우 비싸고 주기적으로 충전을 하여 휴대해야하기 때문에 이용성에 불편함이 있고 실제 트럭이나 버스 같은 대용량 배터리는 Jump Starter가 구동을 하지 못하는 문제점이 있다. 본 논문은 자동차 및 트럭용 Jump Starter의 부피 및 원가를 최소화하면서 일반 운전자들도 휴대 가능한 편리성을 높이며, 대형트럭도 적용 가능한 건전지와 Super Capacitor를 이용한 초소형 저가형 Jump Starter 회로를 제안한다. 기존의 Jump Starter는 납축전지나 리튬전지를 사용하기 때문에, 전체적인 회로의 부피가 크고 무거우며 전체 제품의 원가가 증가하여 제품성이 떨어지는 단점이 있다. 또한 리튬전지를 사용하게 되면 주기적으로 충전을 해야 하기 때문에 소비자가 휴대 및 이용하기에 불편한 문제점도 있다. 반면 제안된 회로는 일반 소모용 건전지로도 Jump Starter 회로 구동이 가능하기 때문에, 운전자의 휴대성이 간편하고 언제 어디서든 소모용 건전지를 구매할 수 있기 때문에 운전자의 휴대성과 이용성이 매우 우수하다. 또한 순간적인 방전이 가능한 Super Capacitor를 이용하여 전체적인 회로의 부피 및 제품의 원가를 최소화 할수 있는 장점을 갖는다. 본 논문에서는 제안된 회로이 이론적인 특성을 분석하고 모의실험을 통해 확인하였으며, 실제 방전된 배터리 및 대형버스에 적용하여 실험을 통해 우수성을 검증하였다.

• Korean Chemical Engineering Research
• /
• v.53 no.3
• /
• pp.269-275
• /
• 2015

The adsorption characteristics of ions were evaluated for the nitrate-selective carbon electrode (NSCE) in accordance with power supply methods. The NSCE was fabricated by coating the surface of a carbon electrode with anion-exchange resin powders with high selectivity for the nitrate ion. Capacitive deionization (CDI) experiments were performed on a mixed solution of nitrate and chloride ion in constant voltage (CV) and constant current (CC) modes. The number of total adsorbed ions in CV mode was 15% greater than that in CC mode. The mole fraction of adsorbed nitrate ion showed the maximum 58%, though the mole fraction was 26% in the mixed solution. This indicates that the fabricated NSCE is highly effective for the selective adsorption of nitrate ions. The mole fraction of adsorbed nitrate was nearly constant value of 55-58% during the adsorption period in CC mode. In the case of CV mode, however, the values increased from the initial 30% to 58% at the end of adsorption. We confirmed that the current supplied to cell is important factor to determine the selective removal of nitrate.

• Journal of Digital Contents Society
• /
• v.14 no.1
• /
• pp.35-40
• /
• 2013

The use of slurry with a mix of abrasives and coolant for making Wire Saw in the photovoltaic industry has sharply increased with the semiconductor wafer. In this paper, the slurry was isolated, purified and dried by microwave drying method with high-purity silicon carbide powder obtained through chemical processing. Dried slurry bulk was first pulverized and chemical treatment was applied to produce powder. The produced slurry powder was then analyzed by going through the following analysis; thermal analysis, particle size analyses: SEM shots, elemental analysis, XRF and XRD. The results of this study found the recovery rate of the power obtained though the chemical processing to be higher than the one obtained from mineral processing. The results anticipate infrastructure building and active responses to increasingly stronger domestic and international environmental regulations through the integration and recycling of large amounts of slurry in the photovoltaic industry.

• Journal of Advanced Marine Engineering and Technology
• /
• v.40 no.10
• /
• pp.894-898
• /
• 2016

Solution plasma is a unique method which provides a direct discharge in solutions. It is one of the promising techniques for various applications including the synthesis of metallic/non-metallic nanomaterials, decomposition of organic compounds, and the removal of microorganism. In the context of nanomaterial syntheses, solution plasma has been utilized to produce carbon nanoparticles and metallic-carbon nanoparticle systems. The main purpose of this study was to synthesize nickel nanoparticles embedded in a matrix of carbon particles by solution plasma in one-step using waste vegetable oil as the carbon source. The experimental setup was done by simply connecting a bipolar pulsed power generator to nickel electrodes, which were submerged in the waste vegetable oil. Black powders of the nickel nanoparticles-embedded carbon (NiNPs/Carbon) particles were successfully obtained after discharging for 90 min. The morphology of the synthesized NiNPs/Carbon was investigated by a scanning electron microscope, which revealed a good dispersion of NiNPs in the carbon-particle matrix. The X-ray diffraction of NiNPs/Carbon clearly showed the co-existence of crystalline Ni nanostructures and amorphous carbon. The crystallite size of NiNPs (through the Ni (111) diffraction plane), as calculated by the Scherrer equation was found to be 64 nm. In addition, the catalytic activity of NiNPs/Carbon was evaluated by cyclic voltammetry in an acid solution. It was found that NiNPs/Carbon did not show a significant catalytic activity in the acid solution. Although this work might not be helpful in enhancing the activity of the fuel cell catalysts, it is expected to find application in other processes such as the CO conversion (by oxidation) and cyclization of organic compounds.