고조파 토오크 함수에 의한 전압원 PAWM인버터의 평가

권우현 경북대학교 전자기술연구소 1988 電子技術硏究誌 Vol.9 No.1

A new HTF(Harmonic torque function) which takes into account the phasor of harmonic current, and which represents torque apple content of induction motor is proposed. Through experiments and computer simulations using direct quadrature two axis model, the proposed HTF is proved to be valid. Applying this function, six-step, SPWM and TPWM pulse-amplitude-controlled inverters are evaluated and compared with each other. A good control strategy for PAWM inverters was chosen from the results. It turns out that TPWM is superior to SPWM in torque ripple content and output voltage amplitude of fundamental wave and six-step is better than PWM when carrier ratio is 9.

고지질 식이 투여를 이용하여 상부위장관내시경 소견으로 진단된 원발성 장림프관 확장증

권우현,황진복,이영환,김용진,Kwon, Woo-Hyun,Hwang, Jin-Bok,Lee, Young-Hwan,Kim, Yong-Jin 대한소아소화기영양학회 1999 Pediatric gastroenterology, hepatology & nutrition Vol.2 No.1

전신 부종을 주소로 내원한 20개월된 남아에서 대변의 ${\alpha}_1$-antitrypsin clearance를 이용하여 단백상실성 장병증으로 진단하고, 상부위장관내시경을 시행하였으나 육안적 및 조직학적 소견상 특기할 만한 진단적 실마리가 관찰되지 않아, 고지질 식이를 투여 후 내시경을 시행하여 육안적, 조직학적 소견상 장림프관 확장증의 특징적인 소견이 확인되어 원발성 장림프관 확장증으로 진단된 증례이다. We experienced a case of primary intestinal lymphangiectasia in a 20-month-old boy, which was confirmed gastrofiberscopically and histologically only after a high-fat meal before the procedure. A characteristic endoscopic finding was the appearance of tiny white dots scattered in the duodenal mucosa, which were proved dilated lymph vessels in the lamina propria on histological examination. Treatment with low-fat diet and medium chain triglycerides supplementation was satisfactory.

Trapezoidal PWM전류원 인버터에서 초소 Speed Ripple을 위한 펄스 수 및 변조도의 결정 ( Selection of Pulses Number and Modulation Index for Minimum Speed Ripple in Trapezoidal CSI-PWM )

권우현,이치환,이창화,구본호 대한전자공학회 1988 대한전자공학회 학술대회 Vol.1988 No.7

충남지역의 고용구조와 인력수급 변동

권우현,김우영,배진한,김진영 한국고용정보원 2017 연구사업보고서 Vol.- No.-

Crystallographic and Magnetic Properties of V2O5-doped Titanium Cobalt Ferrites

권우현,이승화,이재광,채광표 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.4

The effects of vanadium-oxide (V2O5) doping on the crystallographic and magnetic properties of titanium cobalt ferrite, Ti0.2Co1.2Fe1.6O4, are investigated. Ferrite was doped with V2O5 in the range of 0 to 3.0 wt.% by using conventional ceramic methods. Using X-ray diffraction and M¨ossbauer spectroscopy, the formation of crystallized particles was confirmed in ferrite powders. All of the samples showed a single spinel structure, and the lattice parameters were nearly constant as the doping content was increased. The average grain size of the samples increased with the V2O5 concentration up to 2.6 wt.%, and then on further addition it decreased. The average grain size showed a pronounced maximum of about 9.11 μm at 2.6 wt.% V2O5. When x = 0 in x(V2O5) wt.% doped Ti0.2Co1.2Fe1.6O4, the M¨ossbauer spectrum could be fitted with two Zeeman sextets, which is the typical spinel ferrite spectra with A and B sites. However, when x > 0.2, the M¨ossbauer spectrum could be fitted with two Zeeman sextets and one doublet. The doublets can be interpreted as resulting from non-paired Fe ions that do not participate in the A-O-B superexchange process in the spinel structure. From the variation of M¨ossbauer parameters and the absorption area ratio, the cation distribution could be determined. The magnetic behavior of the samples showed that an increase in the V2O5 content up to 2.2 wt.% led to an increase in the saturation magnetization and the coercivity after which a subsequent decrease was observed. The maximum saturation magnetization and coercivity of the samples were 69.0 emu/g and 0.36 kOe, respectively. The effects of vanadium-oxide (V2O5) doping on the crystallographic and magnetic properties of titanium cobalt ferrite, Ti0.2Co1.2Fe1.6O4, are investigated. Ferrite was doped with V2O5 in the range of 0 to 3.0 wt.% by using conventional ceramic methods. Using X-ray diffraction and M¨ossbauer spectroscopy, the formation of crystallized particles was confirmed in ferrite powders. All of the samples showed a single spinel structure, and the lattice parameters were nearly constant as the doping content was increased. The average grain size of the samples increased with the V2O5 concentration up to 2.6 wt.%, and then on further addition it decreased. The average grain size showed a pronounced maximum of about 9.11 μm at 2.6 wt.% V2O5. When x = 0 in x(V2O5) wt.% doped Ti0.2Co1.2Fe1.6O4, the M¨ossbauer spectrum could be fitted with two Zeeman sextets, which is the typical spinel ferrite spectra with A and B sites. However, when x > 0.2, the M¨ossbauer spectrum could be fitted with two Zeeman sextets and one doublet. The doublets can be interpreted as resulting from non-paired Fe ions that do not participate in the A-O-B superexchange process in the spinel structure. From the variation of M¨ossbauer parameters and the absorption area ratio, the cation distribution could be determined. The magnetic behavior of the samples showed that an increase in the V2O5 content up to 2.2 wt.% led to an increase in the saturation magnetization and the coercivity after which a subsequent decrease was observed. The maximum saturation magnetization and coercivity of the samples were 69.0 emu/g and 0.36 kOe, respectively.

Crystallographic and Magnetic Properties of Vanadium-substituted Li-Co-Ti Ferrite

권우현,이재광,이승화,채광표 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.6

The crystallographic and magnetic properties of vanadium-substituted lithium cobalt titanium ferrite, Li0.5+xCo0.2Ti0.2VxFe2.1−2xO4, are investigated. Ferrite was replaced with vanadium in the range of 0.00 to 0.20 in steps of 0.05 and was synthesized by using conventional ceramic methods. Using X-ray diffraction and M¨ossbauer spectroscopy, the formation of crystallized particles was confirmed in Li0.5+xCo0.2Ti0.2VxFe2.1−2xO4 ferrite powders. All of the samples showed a single phase with a spinel structure, and the lattice parameters were nearly constant as the substituted content increased. The average grain size of the samples increased with x. For x = 0 in Li0.5+xCo0.2Ti0.2VxFe2.1−2xO4, the M¨ossbauer spectrum could be fitted with two Zeeman sextets,which is the typical spinel ferrite spectra of Fe3+ with A and B sites. However, for x 0.05, the M¨ossbauer spectra could be fitted with two Zeeman sextets and one doublet. From the variations of the M¨ossbauer parameters and the absorption area ratio, the cation distribution could be determined as (Co0.2−Vx−Fe0.8−x+2)[Li0.5+xCoVTi0.2Fe1.3−x−2]O4. The magnetic behavior of the samples showed that an increase in the vanadium content led to an increase in the saturation magnetization and then to some decrease whereas the coercivity decreased. The maximum saturation magnetization was 44.81 emu/g at x = 0.05, and the maximum coercivity was 120.4 Oe at x = 0.

Crystallographic and Magnetic Properties of Mn1−xZnxFe2O4 Powders

권우현,이승화,채광표,이재광 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.61

Mn1−xZnxFe2O4 powders were fabricated by using a sol-gel method, and their crystallographic and magnetic properties were investigated by using X-ray diffractometry, Mossbauer spectroscopy and vibrating sample magnetometry. All samples were annealed at 500 ℃ in a N2 atmosphere after having been refluxed for 12 hours at 90 ℃ and dried completely. Using the X-ray diffractometer, the formation of single-phased Mn1−xZnxFe2O4 powders was confirmed regardless of the Zn concentration, and the lattice distances decreased a little as the Zn concentration increased. M¨ossbauer spectra measured at room temperature showed two Zeeman sextets in the case of pure Mn ferrite and Mn1−xZnxFe2O4 (x = 0.2 and 0.4) powders. However, M¨ossbauer spectra for x = 0.6 and 0.8 consisted of two six-line sub-spectra and a single quadrupole doublet, which indicated that they were ferromagnetic and paramagnetic: As the Zn concentration increased, the magnetic properties of the Mn1−xZnxFe2O4 powders changed from ferromagnetic to non-magnetic. The saturation magnetization of a pure Mn ferrite powder was 69.5 emu/g and for x = 0.2, it was 65.1 emu/g. The saturation magnetization decreased slowly as the Zn concentration was increased up to 40% and then decreased rapidly to zero. Mn-Zn ferrite powders had a typical soft magnetic property: The coercivity of the pure Mn ferrite powder was 128 Oe. The coercivities of the Mn1−xZnxFe2O4 powders decreased linearly as the Zn concentration was increased.

깻잎의 농산물우수관리제도(GAP) 적용을 위한 수확단계에서 미생물학적 위해요소 분석

권우현,정덕화,이원경,송정언,김경열,심원보,윤요한,김윤식 한국식품위생안전성학회 2012 한국식품위생안전성학회지 Vol.27 No.3

The purpose of this study was to analyze microbiological hazards for plants, cultivation environments and personal hygiene of perilla leaf farms at the harvesting stage. Samples were collected from three perilla leaf farms(A, B, C) located in Gyeongnam, Korea and tested for sanitary indications, fungi and pathogenic bacteria(Escherichia coli O157:H7, Listeria monocytogens, Salmonella spp., Staphylococcus aureus and Bacillus cereus). As a result, total bacteria and coliform in perilla leaf were detected at the levels of 4.4~5.2 and 3.4~4.3 log CFU/g,respectively, but E. coli was not detected in all samples. Among the pathogenic bacteria, B. cereus(perilla leaf:2.0~2.4 log CFU/g, stem: 1.4~2.1 log CFU/g, water: 0.7 log CFU/ml, soil: 4.2~5.0 log CFU/g, hands: 3.0 log CFU/hand, gloves: 2.1~2.4 log CFU/100 cm2, glothes: 1.5~2.8 log CFU/100 cm2) and S. aureus(3.4 log CFU/hand) were detected in all samples and worker's hand from farm A, respectively. However, other pathogenic bacteria were not detected. This study demonstrates that perilla leaf at the harvesting stage was significantly contaminated with microbial hazards.

Mn<SUB>x</SUB>Fe<SUB>3-x</SUB>O₄ 페라이트계의 결정학적 및 자기적 특성

권우현,이재광,이승화,채광표 한국자기학회 2009 한국자기학회 학술연구발표회 논문개요집 Vol.2009 No.5

반탄화된 셀룰로오스와 폴리프로필렌 혼합물의 촉매 열분해

권우현,이형원,박영권 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.1

바이오매스는 화석연료를 대체하여 에너지로 사용이 가능하며 화학원료 물질 생산을 위한 중요한 자원이다. 열분해는 바이오오일이 주 생성물인 방법으로 원료로는 나무, 농업폐기물 등이 있다. 최근 바이오오일의 고품질화를 위해 촉매를 이용한 오일 개질 외에도 열분해 원료의 개선이 시도되고 있다. 열분해 원료의 개선 방법으로는 플라스틱 첨가, 바이오매스의 반탄화 등이 있다. 반탄화된 바이오매스는 친수성 감소, 에너지 밀도 증가 등의 특징을 나타낸다. 이를 통해 바이오오일의 고품질화가 가능하지만 여전히 화석연료 대체, 화학원료 물질 생산에는 부족한 면이 있다. 따라서 추가적으로 탄소와 수소를 공급하면 고품질화가 가능할 것으로 여겨지며, 이것은 탄소와 수소로 이루어진 플라스틱의 첨가를 통해 개선될 것으로 기대된다. 본 연구에서는 제올라이트를 이용한 촉매 열분해를 통해서 원료의 반탄화 효과와 플라스틱과의 혼합열분해를 통한 바이오오일 고품질화를 시도하였다. 열분해 원료로는 모델 물질인 셀룰로오스와 폴리프로필렌을 사용하였다.