• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.379-381
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• 2002

A single CdZnTe detector is tested for suitability in a prototype CT/ SPECT system designed to acquire both emission and transmission data. The detector has the size of 1${\times}$l-cm$^2$ with 4${\times}$4 1.5${\times}$l.5mm$^2$ pixellated anodes. Since the detector is smaller than imaged object, we translated it in an arc centered at the x-ray tube to image larger objects. Pulse counting electronics with very short shaping time (50 ns) are used to satisfy high photon rates in x-ray imaging, and response linearity up to 3${\times}$10$\^$5/ counts per second per detector element is achieved. The energy resolution of 122-keV gamma-ray is measured to be 14%. We have characterized the system performance by scanning a radiographic resolution phantom .and the Hoffman brain phantom. The spatial resolution of CT and SPECT are about 1 mm and 7 mm, respectively.

• Journal of Magnetics
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• v.20 no.4
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• pp.336-341
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• 2015

MnBi alloys were fabricated by arc melting and annealing at 573 K. The heat treatment enhanced the content of the low-temperature phase (LTP) of MnBi up to 83 wt%. The Bi-excess assisted LTP MnBi alloys were used in the hybridization with the Nd-Fe-B commercial Magnequench ribbons to form the hybrid magnets (100-x)NdFeB/xMnBi, x = 20, 30, 40, 50, and 80 wt%. The as-milled powder mixtures of Nd-Fe-B and MnBi were aligned in a magnetic field of 18 kOe and warm-compacted to anisotropic and dense bulk magnets at 573 K by 2,000 psi for 10 min. The magnetic ordering of two hard phase components strengthened by the exchange coupling enhanced the Curie temperature ($T_c$) of the magnet in comparison to that of the powder mixture sample. The prepared hybrid magnets were highly anisotropic with the ratio $M_r/M_s$ > 0.8. The exchange coupling was high, and the coercivity $_iH_c$ of the magnets was ~11-13 kOe. The maximum value of the energy product $(BH)_{max}$ was 8.4 MGOe for the magnet with x = 30%. The preparation of MnBi alloys and hybrid magnets are discussed in details.

• Journal of Magnetics
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• v.19 no.3
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• pp.205-209
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• 2014

$MnBi_{1-x}Ti_x$ (x = 0, 0.4, 0.7, 1) alloys were prepared by arc-melting, followed by heat treatment. X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) were used to measure and investigate the phase structure and magnetic properties. The temperature dependent magnetization curves indicate that the phase transitions between LTP and HTP MnBi occur with heating or cooling in $MnBi_{1-x}Ti_x$ ($x{\leq}0.7$) samples. However, MnTi samples are in $Mn_2Ti$ single-phase, with very low magnetic properties. Furthermore, the coercivity exhibits a positive temperature coefficient. The results show that the optimal content of Ti for the coercivity of $MnBi_{1-x}Ti_x$ alloy is x = 0.4. For MnBi sample, the coercivity reaches a maximum value of 1.13 T at 550 K. However, the remanence and energy product show apparent decrease with the addition of Ti in $MnBi_{1-x}Ti_x$ alloys.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.171-171
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• 1999

We studied the charge redistribution in the Pt-M (M=Cu, Co) alloys by X-ray Absorption Near Edge Spectroscopy(XANES) and X-ray Photoelectron Spectroscopy(XPS). These analysis tools provide us information about the charge transfer in the valence band of intermetallic bonding. The samples were prepared by arc-melting method. After annealing this samples in vacuum for several hours, we cold get the ordered samples, which were confirmed with XRD analysis. the core and valence level energy shift in these system were investigated by Mg $K\alpha$(1253.6eV) x-ray source for Pt-Co alloys and monochromatized Al $K\alpha$ (1486.6eV) for Pt-Cu alloys. Pt L2, L3-edge, and Cu, Co K-edge XANES spectra were measured with the total electron-yield mode detector at the 3Cl beam line of the PLS (Pohang light source0. from the changes of White line (WL) area and the core level shifts of the each metal sites, we can obtain the information about the electrons participating in the intermetallic bonding of the Pt-Cu and Pt-Co alloys.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.83-84
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• 2008

Voltage fluctuation, also known as flicker, is a power quality problem caused by nonlinear loads like electric arc furnace. Since it is interpreted as a variation of the supplied electrical energy, it causes the residential customers to feel much annoyed visually through the lamps. Due to the statistical nature of IEC (International Electrotechnical Commission) short-term flicker severity index, Pst, it is not feasible to pre-evaluate the flicker level using the transient power system simulators such as Sim Power System in Matlab/Simulink. So this paper presents not only how to design the Matlab/Simulink IEC flickermeter to yield the Pst value, which considering electric distribution environments of South Korea, but also how to mitigate the voltage flicker at the Point of Common Coupling (PCC). In order to achieve this, the flicker mitigation efficiencies of various compensating devices, such as Static Var Compensator (SVC), STATCOM will be applied and compared. The simulated result demonstrates which compensating equipment is the most efficient method to mitigate the flicker phenomenon.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.11A
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• pp.1085-1090
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• 2010

Ultra wideband (UWB) technologies have been developed to exploit a new spectrum resource in substances and to realize ultra-high-speed communication, high precision geolocation, and other applications. The energy of UWB signal is extremely spread from near DC to a few GHz. This means that the interference between conventional narrowband systems and UWB systems is inevitable. However, the interference effects had not previously been studied from UWB wireless systems to conventional mobile wireless systems sharing the frequency bands such as Cellular CDMA and Korean PCS. This paper experimentally evaluates the interference from two kinds of UWB sources, namely a direct-sequence spread-spectrum UWB source and an impulse radio UWB source, to a Cellular CDMA and K-PCS digital transmission system. The average frame error rate degradation of each system arc presented. From these experimental results, we show that in all practical cases UWB system can coexist with Cellular CDMA and K-PCS terminal without causing any dangerous interference.

• Journal of Welding and Joining
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• v.28 no.2
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• pp.79-83
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• 2010

In this study, newly developed welding consumables for EGW were welded in EH 36 TM steel plates and their welded joints were evaluated in point of mechanical properties and microstructures compared with imported consumables. Newly developed welding consumables were evaluated as good arc stability and slag fluidity, substantially the same with imported products. The tensile strength of all welded joints were sufficient to meet the requirements specified in a ship’s classification(490~640MPa) and all areas of fracture were heat affected zone(HAZ). Charpy absorbed energy values of all EG welded metals were sufficient to meet the requirements of classification(min. 34J) and those of newly developed wires were evaluated to be better than those of imported wires. As a result observing microstructures of single and tandem EG welded metals through optical and scanning electron microscope (OM&SEM), no grain boundary ferrite(PF(G)) were created in a prior austenite grain boundary and a volume fraction of a fine acicular ferrite were observed very high.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.54.2-54.2
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• 2011

야금학적 정련 공정 중 슬래그 처리, 일방향 응고, 플라즈마-전자기유도용해 공정을 적용한 태양전지용 실리콘 제조 기술에 관한 연구를 수행하였다. 원소재인 금속급 실리콘을 제조하기 위해원재료로 규석, 코크스(Cokes), 숯, 그리고 우드칩(Wood chip)을 사용하였으며, 150kW급 DC 아크로(Arc furnace)를 이용하여 순도 99.8% 금속급 실리콘을 제조하였다. 제조된 용융 상태의 금속급 실리콘은 슬래그와 반응시켜 불순물을 제거하였다. SiO2-CaO-CaF2 계의 슬래그를 이용하였으며, 금속급 실리콘과 슬래그의 질량비 및 반응 시간에 따른 실리콘 불순물 특성을 평가하였다. 이후 고액 계면이 제어 가능한 일방향 응고 장치를 이용하여 금속불순물을 제거하였다. 고액상태의 온도 조건 및 응고 시간에 따른 불순물 농도 변화를 평가하였으며, 순도 6N급의 실리콘을 제조하였다. 마지막 공정으로 스팀 플라즈마 토치와 냉도가니가 적용된 전자기 유도 용해장치를 이용하여 붕소와 인을 제거하였다. 플라즈마 토치 가스로는 아르곤, 스팀, 수소를 이용하였다. 붕소와 인의 제거율은 각각 94%와 96%를 달성하였으며, 최종 순도 6N급의 실리콘을 제조하였다.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.677-678
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• 2006

Pressure risc is an important design factor and affects significantly on the characteristics of gas circuit breakers. For self-blast circuit breakers, the nozzle ablation plays important role in pressure-building up and should be properly considered for the accurate calculation. In this paper, the nozzle ablation is treated as a boundary condition and the pressure is calculated from mass fractions of PTFE and SF6. The amount of the ablated mass of a nozzle is assumed to be proportional to the are energy and the area of nozzle surface that directly touches arc. The calculation result is compared with measured data and shows good agreement with it.

• Journal of Power System Engineering
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• v.4 no.1
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• pp.45-50
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• 2000

Circuit breakers have traditionally employed mechanical methods to interrupt excessive currents. According to power semiconductor technology advances in power electronic device, some mechanical breakers are replaced with solid state equivalents. Advantages of the contactors using semiconductor devices include faster fault interrupting, fault current limiting, no arc to contain or extinguish and intelligent power control, and high reliability. This paper describes the design of a static $100{\pm}10%V$ and 0 to 50A DC self-protected contactor with 85A "magnetic tripping" and 100A interruption current at $2.2A/{\mu}s$ short circuit of load condition using a new power device the HARRIS MCT (600V-75A). The self-protection circuit of this system is designed by the classical ZnO varistor for energy absorption and turn-off snubber circuit ("C" or "RCD") of the MCT.