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통신위성과 지상차량간의 통신에 있어서 가로수로 인한 신호감쇠
홍의석 光云大學校 1988 論文集 Vol.17 No.-
Using Fresnel diffration theory the atteunuation cased by a model tree was calculated to be near 10dB and the maximum fade was found to increase by the logrithm of the number of branches. The results obtained in this paper can be used to reproduce measured data of scattering and fading and to make a quantitative estimate of the influence of parameters such as elevation angle, the distance of scatterers to the mobile and the frequency of tree shadowing.
金範錫,金星坤,韓必熙,朴樹榮,李宜宣,崔祐榮 明知大學校 産業技術硏究所 2009 産業技術硏究所論文集 Vol.28 No.-
In general, LED display system displays the fixed text in ROM. In this paper, we propose the wireless real-time LED display system in which the text can be easily displayed in any text color and display mode by users And the system can be set up in any place by using Zigbee communication.
전기석,홍의석 光云大學校 1976 論文集 Vol.5 No.-
In the design of low cost television receivers when a well-regulated D.C. supply is desired, the Cost of the power supply becomes a major expense. This is especially true when D.C Voltages desired are around 100 Volts and Current require ments exceed 5 amperes. An inexpensive line connected system is described blow which uses an S.C.R. in series with the 120 Volts, 60Hz A.C. line. This system is ideally suited to provide about 50 to 120 Volts D.C. at Currents up to about 0.75 amps. This supply will provide high performance at low cost. Its gain and stability can be tailored to the specific application. All the solid-state components are enough to fit on a small module. It can be an inexpensive, efficient power supply system.
Effectiveness of Pelleting for Inoculating Plant Growth-Promoting Rhizobacteria on Small Seeds
Ui-Gum Kang,Jum-Soon Kang,Si-Lim Choi,Sang-Seok Lee,Jong-Su Kim,Seok-Hee Park 한국토양비료학회 2019 한국토양비료학회지 Vol.52 No.3
The effectiveness of pelleting for inoculating small seeds with plant growth-promoting rhizobacteria (PGPR) was studied. Seeds of sesame cv. Yangbaeckkae and perilla cv. Namcheon were inoculated with Bacillus sp. KR083 and Pseudomonas sp. RRj228 with pelleting material, ‘DPA’ (contained 70% diatomite, 14% perlite, 5% appetite, 5% cow dung, 3% peat, and 3% pea) and stored at refrigerator temperature of 4°C or room temperature of 18 - 20°C for 2 to 7 weeks. While 4°C modestly improved strain survival and growth, crop by strain interaction was substantial. Strain KR083 numbers grew 10 to 13 fold on sesame in 2 to 7 weeks but declined by as much as 78% on perilla across both temperatures. In contrast, strain RRj228 numbers grew 1.7 to 11 fold on perilla but only maintained its numbers on sesame across temperatures and storage times. Strains impacted seed viability differently; while KR083 had no effect, RRj228 decreased germination rate of both sesame and perilla by as much as 20% after 2 weeks of storage of pelleted seeds at 18 - 20°C. Strain KR083 significantly improved root elongation of both crops, but only of sesame when co-inoculated with RRj228. On the other hand, KR083 had lower colonization ability than RRj228 on roots, 19 and 83 % lower on sesame and perilla, respectively. Mixed inoculum, however, significantly improved colonization of both strains on both crops. In field trials, sesame co-inoculated with KR083 and RRj228 yielded 18% higher than non-inoculated control while reducing phytophthora blight infection by 10 and 20% in silty loam and sandy loam soils, respectively. Likewise, Perilla yielded 29% more leaf with mixed inoculation than the non-inoculated, diatomite-pelleted control in the same silty loam soil. Results indicate DPA pelleting as an effective method for small seeded crops when compatible PGPR strains are used as inocula.
Analysis of Phase Error Effects Due to Grid Frequency Variation of SRF-PLL Based on APF
Ui-Seok Seong,Seon-Hwan Hwang 전력전자학회 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.1
This paper proposes a compensation algorithm for reducing a specific ripple component on synchronous reference frame phase locked loop (SRF-PLL) in grid-tied single-phase inverters. In general, SRF-PLL, which is based on all-pass filter to generate virtual voltage, is widely used to estimate the grid phase angle in a single-phase system. In reality, the estimated grid phase angle might be distorted because the phase difference between actual and virtual voltages is not 90 degrees. That is, the phase error is caused by the difference between cut-off frequency of all-pass filter and grid frequency under grid frequency variation. Therefore, the effects on phase angle and output current attributed to the phase error are mathematically analyzed in this paper. In addition, the proportional resonant (PR) controller is adapted to reduce the effects of phase error. The validity of the proposed algorithm is verified through several simulations and experiments.
Analysis of Phase Error Effects between Virtual Two-phase Voltages in SRF-PLL Based on APF
Ui-Seok Seong,Seon-Hwan Hwang 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6
In single-phase grid-connected inverters, precise and fast detection of the phase angle is essential to guarantee the correct generation of the reference signals. In order to detect the phase angle, SRF-PLL system has been widely used in the grid-connected inverter. However, in contrast with three-phase grid-connected inverter system, single-phase grid-connected inverters are difficult to acquire the information of phase angle and frequency. Hence, using an all-pass filter can make a virtual grid voltage, which is shifted 90-degree from the grid voltage. However, the phase error can be generated due to the characteristics of all-pass filter when the grid frequency is varying. In this paper, the effects of output current and synchronous dq-axis voltages due to the phase error caused by non-ideal all-pass filter are analyzed in detail. The effectiveness of the proposed algorithm is verified through simulation and experiment results.