• KIEE International Transactions on Electrophysics and Applications
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• 제5C권1호
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• pp.39-43
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• 2005

We proposed a structure for a 1.55 ㎛ strained separate confinement heterostructure (SCH) multi- quantum well (MQW) superluminescent diode (SLD), having a tapered active region. SLD was fabricated through a two-step procedure: the first step being metal organic chemical vapor deposition (MOCVD) and the second-step being liquid phase epitaxy (LPE). We used a 15 laterally tilted stripe and window region to suppress the lasing action of the SLD. The performance of the SLD showed output power of 11 mW with no lasing under 200 mA pulse driving. The full-width at half-maximum was 42 nm at 200 mA, 25℃.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제30회 추계학술대회
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• pp.42-48
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• 1999

An experimental study was performed to discover the effect of environment on the tribological behavior of Si-incorporated diamond-like carbon(Si-DLC) film slid on a steel ball. The films were deposited on Si(100) wafers from radio-frequency glow discharge of mixtures of benzene and dilute silane gases. Experiments using a ball-on-disk test-rig was performed under vacuum, dry air and ambient air conditions. It was observed that coefficient of friction was decreased as the environmental condition changes from vacuum, to dry air. It was also observed that the coefficient of friction decreased with increasing silicon concentration in the film. Chemical analyses of debris suggested that the low and stable friction coefficient is closely related to the silicon rich oxide debris and the rolling action.

• 한국레이저가공학회지
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• 제4권2호
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• pp.13-19
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• 2001

When a high-power laser beam is irradiated on the surface of material, it is well known that a cavity, called a keyhole induced by the pressure action of the vapor plume, is generated in the molten material. This paper describes the interaction between a pulsed CO$_2$ laser beam and water. The laser-beam is used to generate and maintain a conical depression in the water surface similar to the keyhole created during laser penetration welding. Experimental results show that the depth of laser-beam penetration is limited by hydrodynamic instability. The instability of the surface cavity can be understood by the capillary instability of a hollow jet. Theoretical computation of the steady keyhole shape has been performed. modifying the model suggested by Andrews et al. (1976). The model predicts the qualitative behavior of the keyhole but significantly underestimates the average diameter.

• Tribology and Lubricants
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• 제16권3호
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• pp.188-193
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• 2000

An experimental study was performed to discover the effect of environment on the tribological behavior of Si-incorporated diamond-like carbon(Si-DLC) film slid on a steel ball. The films were deposited on Si(100) wafers by a radio-frequency glow discharge of mixtures of benzene and dilute silane gases. Experiments using a ball-on-disk test-rig was performed in vacuum, dry air and ambient air conditions. It was observed that coefficient of friction decreased as the environment changed from vacuum, to dry air. Chemical analyses of debris suggested that low and stable friction is closely related to the formation of silicon-rich oxide debris and the rolling action.

• 한국분말재료학회지
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• 제27권6호
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• pp.464-467
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• 2020

Nickel nanopowders are obtained by the spark discharge method, which is based on the evaporation of the electrode surface under the action of the discharge current, followed by vapor condensation and the formation of nanoparticles. Nickel electrodes with a purity of 99.99% are used to synthesize the nickel nanoparticles in the setup. Nitrogen is used as the carrier gas with a purity of 99.998%. XRD, TEM, and EDX analyses of the nanopowders are performed. Moreover, HRTEM images with measured interplanar spacings are obtained. In the nickel nanopowder samples, a phase of approximately 90 wt% with an expanded crystal lattice of 6.5% on average is found. The results indicate an unusual process of nickel nanoparticle formation when the spark discharge method is employed.

• 한국지하수토양환경학회지:지하수토양환경
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• 제18권6호
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• pp.8-17
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• 2013

The contamination of chlorinated ethenes at an industrial complex, Wonju, Korea, was examined based on sixteen rounds of groundwater quality data collected from 2009 to 2013. Remediation technologies such as soil vapor extraction, soil flushing, biostimulation, and pumping-and-treatment have been applied to eliminate the contaminant sources of trichloroethylene (TCE) and to prevent the migration of TCE plume from remediation target zones. At each remediation target zone, temporal monitoring data before and after the application of remediation techniques showed that the aqueous concentrations of TCE plume present at and around the main source areas decreased significantly as a result of remediation technologies. However, the TCE concentration of the plumes at the downstream area remained unchanged in response to the remediation action, but it showed a great fluctuation according to seasonal recharge variation during the monitoring period. Therefore, variations in the contaminant flux across three transects were analyzed. Prior to the remediation action, the concentration and mass discharges of TCE at the transects were affected by seasonal recharge variation and residual DNAPLs sources. After the remediation, the effect of remediation took place clearly at the transects. By tracing a time-series of plume evolution, a greater variation in the TCE concentrations was detected at the plumes near the source zones compared to the relatively stable plumes in the downstream. The difference in the temporal profiles of TCE concentrations between the plumes in the source zone and those in the downstream could have resulted from remedial actions taken at the source zones. This study demonstrates that long term monitoring data are useful in assessing the effectiveness of remediation practices.

• 한국초전도ㆍ저온공학회논문지
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• 제3권2호
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• pp.15-20
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• 2001

This paper describes a model flux pump experiment recently performed at the MIT Francis Bitter Magnet Laboratory. The results of the model flux pump will be used in the development of a prototype flux pump that will be couple to a high-temperature superconductor (HTS) insert coil of a high-field NMR (Nuclear Magnetic Resonance) magnet, Such an HTS insert is unlikely to operate in persistent model because of the conductors low index(n) The flux pump can compensate fro field decay in the HTS insert coil and make the insert operate effectively in persistent mode . The flux pump, comprised essentially of a transformer an two switches. all made of superconductor, transfers into the insert coil a fraction of a magnetic energy that is first introduced in the secondary circuit of the transformer by a current supplied to the primary circuit. A model flux pump has been designed. fabricated, and operated to demonstrate that a flux pump can indeed supply a small metered current into a load superconducting magnet. A current increment in the range of microamperes has been measured in the magnet after each pumping action. The superconducting model flux pump is made of Nb$_3$ Sn tape, The pump is placed in a gaseous environment above the liquid helium level to keep its heat dissipation from directly discharged in the liquid: the effluent helium vapor maintains the thermal stability of the flux pump.

• Journal of Magnetics
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• 제17권1호
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• pp.9-12
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• 2012

Attempts to dope carbon nanotube (CNT) with impurities in order to control the electronic properties of the CNT is a natural course of action. Boron is known to improve both the structural and electronic properties. In this report, we study the field emission properties of Boron-doped double-walled CNT (DWCNT). Boron-doped DWCNT films were fabricated by catalytic decomposition of tetrahydrofuran and triisopropyl borate over a Fe-Mo/MgO catalyst at $900^{\circ}C$. We measured the field emission current by varying the doping amount of Boron from 0.8 to 1.8 wt%. As the amount of doped boron in the DWCNT increases, the turn-on-field of the DWCNT decreases drastically from 6 V/${\mu}m$ to 2 V/${\mu}m$. The current density of undoped CNT is 0.6 mA/$cm^2$ at 9 V, but a doped-DWCNT sample with 1.8 wt% achieved the same current density only at only 3.8 V. This shows that boron doped DWCNTs are potentially useful in low voltage operative field emitting device such as large area flat panel displays.

• 한국응용곤충학회지
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• 제4권
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• pp.11-18
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• 1965

Phenylmercuric 8-Oxyquinolinate의 광범위한 식물병원균에 대한 살균작용, 식물의 수분증산억제작용, 식물에 대한 약해작용, Gas작용 및 자외선에 의한 경시변화에 관해 실험을 행하였으며, 그 결과를 요약하면 다음과 같다. (1) 포자발아억제작용은 P.M.A.보다 약간 불량한 결과를 보이며, 균사생장억제작용은 P.M.A. 보다도 양호하였다. (2) 식물의 수분증산억제작용은 초기에는 8-Hydroxyquinoline sulfate가 P.M.Q.보다도 강한 억제작용을 나타내었으나, 끝에 가서는 반대로 P.M.Q가 Oxine sulfate보다도 강한 작용을 나타냈다. (3) 수도종자의 발아, 발근에 미치는 영향은 P.M.A. 보다 약해가 적었고 수도 및 대두의 유식물의 경엽(40ppm 처리)에도 약해가 없었다. (4) 식불병원균에 대한 Gas효과에 의한 살균력은 P.M.A.보다 적었다. (5) 자외선에 의한 영향은 생물학적인 변화와 화학적인 변화가 거의 일치하였으며 P.M.Q.는 P.M.A.보다도 훨씬 자외선에 안정하였다. 이상의 결과로 보아 본약제는 광범위한 식물병원균에 대해 살균작용을 가지고 있고 식물의 수분증산도 억제시키며 이화학적인 안정성을 가진 유망한 살균제가 될 것으로 생각된다.

• 대한화학회지
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• 제50권2호
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• pp.141-152
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• 2006

이 연구에서는 고등학교 화학II 교과서의 ‘용액' 단원에 대한 내용을 입자 수준으로 표현한 컴퓨터 보조 수업자료를 개발하고 그 효과를 고등학교 1학년과 2학년 학생들에게 적용하여 그 효과를 알아보았다. 개발된 내용은 교과서에서 제시한 ‘용액' 단원의 주요 내용으로 용해, 증기압, 끓는점과 어는점의 변화, 삼투현상 등으로 구성되었다. 이 연구에서는 애니메이션과 시뮬레이션을 이용하여 자료를 개발하였다. 이 자료에서는 특히 용액에서 일어나는 현상에 대한 주요 개념을 입자 관점에서 이해할 수 있도록 중점을 두었 다. 용액의 여러 현상들을 용액의 총괄성으로 단순화하지 않고, 용매와 용질 사이의 인력 개념으로 설명하였다. 용액과 관련된 자료의 제작은 플래시 5.0과 플래시 6.0의 Action Script를 이용하였다. 개발한 자료를 고등학교 학생들에게 투입한 결과, 통계적으로 유의미하게 개념 향상을 나타내었으며 특히 고등학교 1학년은 과도기와 형식적 조작기 학생들에게, 그리고 고등학교 2학년의 경우에는 형식적 조작기 학생들과 자연계열 학생들에게서 그 효과가 크게 나타났다.