• 대한금속재료학회지
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• 제47권11호
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• pp.754-758
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• 2009

Dense $5Cu_{0.6}Fe_{0.4}-Al_{2}O_{3}$ composite was consolidated from mechanically synthesized powders by high frequency induction heating method within 2 min. Consolidation was accomplished under the combined effects of a induced current and mechanical pressure. Dense $5Cu_{0.6}Fe_{0.4}-Al_{2}O_{3}$ with relative density of up to 95% was produced under simultaneous application of a 80 MPa pressure and the pulsed current. Fracture toughness and hardness of the composite are $7.6MPa{\cdot}m^{1/2}$ and $844kg/mm^{2}$ respectively.

• 한국자원식물학회지
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• 제25권4호
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• pp.456-464
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• 2012

본 연구는 야생 참당귀의 무균묘 확보, 대량생산체계 확립 및 품종개발을 위해 기내발아와 기관유도에 미치는 PGRs의 영향을 알아보고자 실시하였다. 종자발아 실험은 전처리로 $GA_3$ 침지시간(0, 24h, 48h, 72h) 및 종자의 처리 방법(대조구, 기계적가상 처리, 표면 메탄올 가열 소독법)을 달리하여 실시하였다. 그 결과 $GA_3$에 침지시키지 않고 메탄올 가열법으로 처리한 종자를 0.5 mg/L $GA_3$가 첨가된 배지에서 가장 높은 발아율(15%)을 보였으나 저조하여 발아율 향상을 위해 초음파(frequency 80 KHz) 및 PGRs($GA_3$, BA, TDZ)를 처리하였다. 그 결과 초음파 처리 후 메탄올 가열법으로 처리 한 종자를 0.1 mg/L $GA_3$가 첨가된 배지에 치상하여 발아율(60%)을 증진 시킬 수 있었다. 기내 발아된 식물체로부터 기관유도에 미치는 PGRs(2,4-D, NAA, TDZ, BA)의 영향을 살펴본 결과 캘러스 유도는 줄기, 뿌리, hypocotyl을 1.0 mg/L NAA + 0.5 mg/L BA 처리구에 치상하였을 때 높은 유도율을 보였다. 신초와 뿌리유도는 각각 hypocotyl(PGRs 무첨가)과 뿌리(0.1 mg/L NAA 첨가구)에서 효율적으로 분화되었다. 또한 줄기(1.0 mg/L 2,4-D 처리구)와 hypocotyl(0.1 mg/L NAA 처리구) 조직에서 체세포배가 발생되어 MS 기본배지에 계대배양하여 정상적인 식물체로의 육성이 가능하였다. 본 연구를 통해 무균묘 확보 및 대량생산 체계를 확립하였으며 이를 통해 신품종 개발에 유용할 것으로 판단된다.

• The Plant Pathology Journal
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• 제29권3호
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• pp.350-355
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• 2013

Plants protect themselves from diverse potential pathogens by induction of the immune systems such as systemic acquired resistance (SAR). Most bacterial plant pathogens thrive in the intercellular space (apoplast) of plant tissues and cause symptoms. The apoplastic leaf exudate (LE) is believed to contain nutrients to provide food resource for phytopathogenic bacteria to survive and to bring harmful phytocompounds to protect plants against bacterial pathogens. In this study, we employed the pepper-Xanthomonas axonopodis system to assess whether apoplastic fluid from LE in pepper affects the fitness of X. axonopodis during the induction of SAR. The LE was extracted from pepper leaves 7 days after soil drench-application of a chemical trigger, benzothiadiazole (BTH). Elicitation of plant immunity was confirmed by significant up-regulation of four genes, CaPR1, CaPR4, CaPR9, and CaCHI2, by BTH treatment. Bacterial fitness was evaluated by measuring growth rate during cultivation with LE from BTH- or water-treated leaves. LE from BTH-treatment significantly inhibited bacterial growth when compared to that from the water-treated control. The antibacterial activity of LE from BTH-treated samples was not affected by heating at $100^{\circ}C$ for 30 min. Although the antibacterial molecules were not precisely identified, the data suggest that small (less than 5 kDa), heat-stable compound(s) that are present in BTH-induced LE directly attenuate bacterial growth during the elicitation of plant immunity.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.287-290
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• 2005

Once hot forgings for automotive parts such as wheel bearing flange to which cyclic asymmetric bending stress is continuously applied are produced, it is necessary to control their microstructure to obtain superior mechanical properties. It is however hard to control the microstructure uniformly because the strength is reduced as coarsening of ferrite grains. To investigate the microstructural alteration according to process variables during hot working, the variation of the ferrite grain size was studied by utilizing of the computer aided servo-hydraulic Gleeble tester which is hot deformation behavior reproduction equipment. In addition, the effect of the ferrite grain size of raw material on the austenite grain behavior of hot forgings was also examined. The rolling contact fatigue resistance of the induction hardened SAE 1055 steel was compared with the occasion of the same condition of SAE52100 bearing steel. As a result, it was confirmed that the ferrite grain sizes of the forgings depend on the heating temperature and cooling start temperature during hot forging and cooling processes. The induction hardened SAE1055 steel showed a superior rolling contact fatigue resistance to the induction hardened SAE52100 steel. The reason is that SAE1055 steel is freer from the material defect such as segregation than the comparative steel.

• 대한금속재료학회지
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• 제48권11호
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• pp.974-980
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• 2010

Various types of steel, namely, 0.35C, 0.2C-Cr, and 0.2C-Cr-Mo steels, were quenched and tempered by high-frequency induction heat treatment. The type, size, and spheroidization of the carbides varied depending on the tempering temperatures ($450{\sim}720^{\circ}C$). During the tempering process, the carbide was precipitated in the martensite matrix. The 0.35C, 0.2C-Cr, and 0.2C-Cr-Mo steels contained carbides that were smaller than 120 nm. The carbide was spheroidized as the tempering temperature increased. Owing to the fine microstructure and spheroidization of the carbides, all three steels had a high tensile strength as well as yield ratio and reduction of area. In the case of the 0.2C-Cr steel, the use of Cr as an alloying element facilitated the precipitation of alloyed carbides with an extremely small particle and resulted in an increase in the spheroidization rate of the carbides. As a result, a large reduction of area was achieved (>70%). The 0.2C-Cr-Mo steel had the highest tensile strength because of the high hardenability that can be attributed to the presence of alloying elements (Cr and Mo). Quenching and tempering steels by induction heat treatment resulted in a high strength of over 1 GPa and a large reduction of area (>70%) because of the rapid heating and cooling rates.

• 대한금속재료학회지
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• 제49권8호
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• pp.614-618
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• 2011

Nanopowders of MgO, $Al_2O_3$ and $SiO_2$ were made by high energy ball milling. The rapid sintering of nanostructured $MgAl_2O_4-Mg_2SiO_4$ composites was investigated by a high-frequency induction heating sintering process. The advantage of this process is that it allows very quick densification to near theoretical density and inhibition of grain growth. Nanocrystalline materials have received much attention as advanced engineering materials with improved physical and mechanical properties. As nanomaterials possess high strength, high hardness, excellent ductility and toughness, undoubtedly, more attention has been paid for the application of nanomaterials. Highly dense nanostructured $MgAl_2O_4-Mg_2SiO_4$ composites were produced with simultaneous application of 80MPa pressure and induced output current of total power capacity (15 kW) within 2min. The sintering behavior, gain size and mechanical properties of $MgAl_2O_4-Mg_2SiO_4$ composites were investigated.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.238-242
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• 2004

The paper describes an automatic frequency control current-fed inverter for forging applications. The IGBT in series with diodes as its switching devices in the inverter circuit which is of full-bridge type. The operating frequency is automatically tracked to maintain a small constant leading phase angle when load parameters change. The load voltage is controlled to protect the switches. The output power can be adjusted by varying the input current from phase controlled rectifiers which is a part of current source. The system has been operated at 15-17 kHz. The output power transferred to the load is 1,595 watts. It can heat the steel work pieces with 15 mm diameter and 120 mm long from room temperature to approximately 1100 $^{\circ}C$ within 20 seconds with 0.97 leading power factor on the input side.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2013년도 추계학술대회 논문집
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• pp.224-226
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• 2013

본 논문은 유도가열 시스템의 자성체 판별 알고리즘을 제안한다. 코일의 형상 및 구성에 따른 임피던스를 수학적으로 분석하여 자성체와 비자성체 동시 가열을 위한 유도 코일을 능동적으로 설계 한다. 또한 인버터 출력전압과 부하 전류를 센싱하여 계산한 임피던스 값과 수식으로 구한 부하 임피던스를 비교해 가열 용기의 재질을 판별한다. 제안된 알고리즘을 통해 자성체 및 비자성체 유도가열을 하나의 공진형 인버터로 구현할 수 있다. 제안된 판별법은 시뮬레이션을 통해 검증한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1991년도 추계학술대회 논문집 학회본부
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• pp.227-230
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• 1991

This paper discussed with a voltage-fed Type high frequency inverter with simple main circuit and high efficiency. The proposed inverter is proper as a high frequency inverter of home applications applied with induction heating principle of high frequency. and also, this paper proposed an computer analysis for resonant L and C.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1990년도 추계학술대회 논문집 학회본부
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• pp.326-331
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• 1990

In the vector-controlled induction machine drive, mechanical sensors restrict the wide applications of high performance AC drives. So in resent years, many papers have been presented which doesn't need mechanical sensors, named by sensorless vector control. But sensorless control has a few serious problem, one of which Is poor speed estimation in case of incorrect rotor resistance (Rr) information. This paper describes the stator flux orientation speed control strategy with the speed estimation algorithm. and the method of adapting Rr change due to thermal heating. By proposed method. We can acquire precise speed estimation and higher performance.