• Proceedings of the KAIS Fall Conference
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• 2002.05a
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• pp.52-54
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• 2002

본 연구는 고특성 소결자석 제조용 strip-cast 합금을 개발하기 위한 기초단계 연구로서 파양한 조건을 통해 strip-cast 합금을 제조한 후, 제조조건이 합금의 미세조직 형성에 미치는 영향을 조사하였다. 조성이 Nd/sub 15/Fe/sub 77/B/sub 8/인 strip-cast 합금을 다양한 방법으로 제조한 결과, wheel speed 즉, 냉각속도가 5 m/s 이하에서 strip 표면에 수직한 방향으로 수지상정이 잘 발달한 것을 발견하였으나, 그 이상의 냉각속도에서는 수지상정이 붕괴되며 미세한 결정질로만 구성된 것으로 관찰되었다. 따라서 잘 발달된 수지상정을 얻기 위해서는 냉각속도를 5 m/s로 유지해야 함을 알 수 있었다 이 때 수지상정간 간격은 약 4-7㎛로써 고특성 소결자석의 기준에 잘 부합되었다. 한편 XRD 분석결과, 냉각속도 5 m/s이하에서는 <001> 방향으로 뚜렷하게 preferred orientation이 일어난 것을 확인하였으며, 이것은 strip 합금의 분쇄 및 소결시에 결정립 배향성에 유리하게 작용하여 최종 소결자석의 자기적 특성 향상에 기여할 것으로 예상된다.

• Journal of the Korean Magnetics Society
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• v.14 no.5
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• pp.196-200
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• 2004

In order to improve dendritic formation of Nd$_2$Fe$\_$14/B phase in the strip-cast Nd-Fe-B alloys that are frequently used for production of high energy sintered magnets, effect of small substitutional additives such as Cu (0.3～1.0 at. %) and Co (0.5～1.5 at.%) on the phase formation and microstructures of the strip-cast alloys based on Nd$\_$14/Fe$\_$80/B$\_$6/ were investigated. As the amount of Cu addition increased, formation of Nd$_2$Fe$\_$14/B dendrites along the direction normal to the strip surface was suppressed with the reduction of the strip thickness mainly due to the increase of fluidity of the melt. However, both the dendrites and their <001> preferred orientation along the direction normal to the strip surface were improved with the increase of the strip thickness as the amount of Co addition increased. The dendrites became finer after small amount of Cu or Co was added. While small copper additions tended to stabilize the formation of primary Fe, small cobalt additions suppressed it. When small amount of Zr was added, however, the dendrite structures were totally collapsed with excessive grain growth of Nd$_2$Fe$\_$14/B.

• Proceedings of the Korean Magnestics Society Conference
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• 2000.09a
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• pp.379-380
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• 2000

• 전기의세계
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• v.9
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• pp.59-71
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• 1962

전력사업은 시설산업으로서 타기업에 비해 장기간의 공기와 막대한 자금이 소유되며 광대한 고정시설을 보유한다. 따라서 전기사업에 있어서의 장기계획은 장기간의 수요동향을 파악하여 이 수요에 맞는 시설계획 및 자금계획을 수립하여 장래수합 및 수지균형을 도모해야한다. 따라서 전원개발계획수립에 있어서 가장 핵심적인 역할을 하는 것은 수요상정이라 할 수 있을 것이다. 단, 이 수요상정을 그릇치면 중대한 결과가 초래되는것이니 적극적인 상정에 기인하는 수요를 상회하는 발전시설은 자금의 사장을 의미하는 것이며 소극적인 상정은 반대로 부가제한을 가져올 것이다. 수요상정에 따라 개발순위 및 건설공사계획표가 작성되어 가동일자가 결정되며 이에 기준하여 연료수급계획이 작성된다. 일면 이 전력을 반송하고 수용에 반응하기 위한 송변배전시설계획이 병행작성 수립되어야 한다. 최종적으로 자금계획이 성안되어 이와같은 계획을 경제적으로 뒷받침하여야 함은 물론이다. 개발계획수립에 있어서 고려해야 할 점은 이외에도 예비출력 및 단위기용량의 결정, 개발순위에 관련되는 수화력개발의 우위성에 관한 검토, 부가곡선을 통한 부가율 및 용량율의 결정, 등 실로 광범하며 이와 같은 제반요소를 집대성한 것이 전원개발계획이다. 본고에서는 우리나라 5개년전원개발계획을 설명하고 전원개발계획에 관련된 제반문제중 및가지 문제점에 한정하여 이를 약술하고자 한다.

• Journal of Korean Society of Transportation
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• v.23 no.7 s.85
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• pp.53-61
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• 2005

The Seoul City Government recently reformed the entire public transport system in an effort to prevent further deterioration in urban bus system's performance and service level. To analyze into impact on the productivity of Seoul's urban bus firms, this paper measures firm-level technical efficiency and productivity change with data envelopment analysis and Malmquist index approach. The paper then conceptualizes that these forms produce three kinds of output (bus-kilometers, passengers, or bus-kilometers and passengers) using five inputs (driver, maintenance, management, vehicle and fuel). The findings show that most (over one half) firms experienced a decline (an improvement) in productivity in the case of specifying only bus-kilometers (passengers) as output. As a result, it is discovered that an average firm had no change in productivity in the case of combining bus-kilometers and passengers as output. This is because the efficiency of an average firm declined due to increase in employees per bus and to an decrease in kilometers per bus. while its effectiveness improved due to an increase in passengers per bus which was caused by an increase in routes and a change in fare structure.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.3
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• pp.102-108
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• 2018

The objective of this study is to develop the mechanical properties of an AlSiCu aluminum alloy using the two-step solution heat treatment. The microstructure of the gravity casting specimen represents a typical dendrite structure with a secondary dendrite arm spacing (SDAS) of 40 um. In addition to the Al matrix, a large amount of coarsen eutectic Si phase, $Al_2Cu$ intermetallic phase, and Fe-rich phases is generated. The eutectic Si phases are fragmented and globularized with the solution heat treatment. The $Al_2Cu$ intermetallic phase is also resolutionized into the Al matrix. The $2^{nd}$ solution temperature at $525^{\circ}C$ may be an optimal condition to enhance the mechanical properties of the AlSiCu aluminum alloy.

• Journal of the Korean Magnetics Society
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• v.10 no.1
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• pp.1-6
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• 2000

Amorphous Fe$_{79.7}$Si$_{9.3}$B$_{9.7}$Ni$_{1.4}$ ribbon alloys were fabricated by a single roll method. To enhance D. C. bias properties, the magnetic and micro-structural changes have been investigated as the variation of annealing time and condition. The D. C. bias properties were found to be directly related to micro-structural changes. Primary ${\alpha}$-Fe dendrites with 200∼300 nm showed the best D. C. bias properties, which resulted from the magnetic domain wall pinning effect. Due to the differences of cooling rate, the growth shape and distribution of the dendrites is divided into two areas.

• Journal of Welding and Joining
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• v.17 no.2
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• pp.104-111
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• 1999

The interfacial microstructure and bond strength were examined for WC-Co/Cu/SM45C steel join using a nickel-plated copper in vacuum at 1323K for 0.6ks∼3.6ks. After bonding, microstructure in bonding interface was observed by OM(Optical Microscopy), SEM(Scanning Electron Microscopy) and EPMA(Eelectron Probe Micro Analyzer). The oil cooling was carried out at 353K, the cooling rate in air and furnace was 22K/s and 4.4K/s. respectively. It was found that dendritic widths increased with the content of cobalt and bonding times at 1323K. As a whole, bond strength values at the same bonding condition decreased in this order: WC-13wt.%Co/SM45Csteel. WC-8wt.%Co/SM45Csteel and WC-4wt.%Co/SM45Csteel. The bond strength of WC-13wt.%Co/S45C steel joint in oil cooling was 273MPa. This value was greatly higher than those of 125MPa in furnace cooling and 93MPa in air cooling at 1323K for 0.6ks. The bond strength values were found to be closely associated with the content of cobalt in WC-Co and cooling rate.

• Sleep Medicine and Psychophysiology
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• v.1 no.1
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• pp.76-86
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• 1994

Objectives: This research was performed in order to observe the neuropsychological implication and functional anatomical source of event related potentials(ERP) by studying of correlations between event related potentials and neuropsychological tests. Methods: The latency and voltage of P100 of visual evoked potential (VEP), and N120 and P300 of event related potentials were studied in 56 patients and their correlations with neuropsychological tests were computed. Results: The tests showing significant correlation with latency P100 were visual continous performance test(VCPT) and contingent continous performance test(CCPT) without any significant correlation with voltage of P100. In latency of N120 category test and verbal IQ of KWIS showed significant correlation, and in voltage of N120, finger tapping test, VCPT, CCPT and digit symbol test displayed significant correlations. The latency of P300 had significant correlation with trail making A test and Stroop test. In the voltage of P300 significant correlations were shown with trail making B test, digit symbol test and Wechsler memory scale, finger tapping test, stroop test, VCPT and CCPT. Conclusion : N120 may be considered to reflect the function of medial frontal lobe and P300 may be considered to be developed from the subcortical connection of medial temporal lobe, hippocampus, thalamus, basal ganglia and medial frontal lobe.

• Korean Journal of Metals and Materials
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• v.49 no.7
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• pp.570-576
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• 2011

The shape of a dendrite tip has long been approximated by a paraboloid of revolution, but many attempts have been made as well to more accurately match the dendrite tip profile using other mathematical functions: power function, 4th order polynomial, and hyperbolic function. In the present work, dendrite tip shapes were matched by parabolic function. The differences between the dendrite tip shapes of pivalic acid(PVA)-ethanol(Eth) and succinonitrile(SCN)-salol systems, characterized by anisotropic and isotropic solid-liquid interfacial properties, respectively, were quantitatively treated using shape parameters. The PVA-Eth system showed a slightly higher Z/R value than the SCN-salol system, their Z/R values lying in the range 2-4. (Z is the distance from the tip beyond which the parabolic fit starts to deviate from the profile, and R the tip radius.) ${\lambda}_P$ is the distance from the tip beyond which side branching starts to appear, and is larger in the PVA-Eth system than the SCNsalol system. ${\lambda}_P$ is different for both sides of the 2-dimensional dendrite profile. The difference of ${\lambda}_P$ between both sides of the dendrite is larger for PVA-Eth system than for SCN-salol, implying that the dendrite of PVA-Eth is less symmetric than that of SCN-salol.