• Journal of the Korean Physical Society
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• 제73권10호
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• pp.1410-1419
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• 2018

A skier's motion was analyzed by a simple model consist of point mass m and a single rod connected to a single ski plate. We studied the conditions for the stable ski turn as functions of the linear velocity and the radius of the turn. The solutions for the stable ski turn in our model do not require any extra skier's movement to complete a stable circular turn. The solution may then give the skier the most comfortable skiing method without any active movement to control the ski. The generalized force supporting the point mass from the ski plate was calculated. We obtained the force from the ground (rebound force) without any geometrical structure of the ski plate. Adding an active movement to the direction of the ski plate, the conditions for the stable ski turn were also analyzed. Our result gives some insight for the skier who wants to develop technique.

• 한국지구과학회지
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• 제28권7호
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• pp.825-837
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• 2007

한국 국립해양조사원의 수심자료와 미국 NIMA((National Imagery and Happing Agency)의 수치지형자료를 바탕으로 우리나라 일원에서 측정한 중력의 지형보정을 위한 위도 및 경도 간격이 각각 $3"{\times}3"$)인 지형자료를 재편집하였다. 이 자료를 바탕으로 지구 곡률을 고려한 정밀 지형보정값을 계산하기 위한 알고리즘을 개발하였고, 중력측정점으로부터 반지름 166.735 km인 원 내부에 대한 지형보정값을 계산하는 Fortran프로그램을 작성하였다. 이 알고리즘 및 프로그램을 이용하여 남한 전역에 대한 지형보정값을 계산하였다. 그 결과 최대값은 56.508 mGal 이고 평균값은 4.539 mGU이다.

• 한국기계가공학회지
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• 제10권4호
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• pp.38-43
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• 2011

Industrial reducer is in general use to Deck Crane. High-precision and high-efficient reducer is minimized the power-loss and energy-loss of a machine. So it contribute the price reduction and life extension. Reducer is usually using the Planetary gear reducer. Planetary gear reducer is composed the sun gear, planet gear, internal gear and casing. Industrial reducer's wear and breakage have a short-life. To solve this problem, it is using the profile-shifted-gear or tooth modification. This study was carried out the effect of addendum modification coefficient on tooth fillet bending strength to planetary reducer. Tooth fillet bending stress is calculate. And all parameter were expressed the function of addendum modification coefficient. And then stress concentration factor of tooth fillet curve was express the function of addendum modification coefficient using comparison between theory and finite element analysis.

• 대한수학회논문집
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• 제12권4호
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• pp.881-893
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• 1997

E. M. Silvia introduced the class $S^\lambda_\alpha$ of $\alpha$-spirallike functions f(z) satisfying the condition $$ (A) Re[(e^{i\lambda} - \alpha) \frac{zf'(z)}{f(z)} + \alpha \frac{(zf'(z))'}{f'(z)}] > 0, $$ where $\alpha \geq 0, $\mid$\lambda$\mid$ < \frac{\pi}{2}$ and $$\mid$z$\mid$ < 1$. We will generalize Silvia class of functions by formally replacing f(z) in the denominator of (A) by a spirallike function g(z). We denote the new class of functions by $Y(\alpha,\lambda)$. In this note we obtain some results for the class $Y(\alpha,\lambda)$ including integral representation formula, relations between our class $Y(\alpha,\lambda)$ and Ziegler class $Z_\lambda$, the radius of convexity problem, a few coefficient estimates and a covering theorem for the class $Y(\alpha,\lambda)$.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2009년도 춘계학술대회 논문집
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• pp.1977-1983
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• 2009

This paper described partial discharge(PD) patterns depending on types of insulation defects in CNCO-W cable(Concentric Neutral Closs-linked Polyethylene Insulated Polyolefin-Water Proof Sheathed Power Cable). The PD measurement system consists of a coupling network, a detection impedance, and a low noise amplifier. A 16 bit, 250 MS/s data acquisition system was used to analyze PD patterns. To simulate insulation defects in a power cable, a needle with the curvature radius of $10{\mu}m$ was inserted into the insulation part. We measured phase ($\Phi$), magnitude (q), and counts (n) of PD pulse for the defects, and classified PD patterns using the PRPD (phase Resolved Partial Discharge) method. From the analysis of acquired PD signals, we could find that a unique PD pattern is formed according to the types of defect.

• 천문학회보
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• 제46권2호
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• pp.78.3-79
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• 2021

Coronal Diagnostic Experiment (CODEX) is a diagnostic coronagraph developed by the Korea Astronomy and Space Science Institute and the NASA Goddard Space Flight Center (GSFC) to be deployed in 2023 on the International Space Station (ISS). It is designed to obtain simultaneous measurements of electron density, temperature, and velocity in the 2.5 - 10 solar radius range using multiple filters. The filters are mounted in two filter wheel assemblies (FWAs), which have five filter positions each. One position of each FWA is occupied by windows, and remaining eight positions are occupied by three bandpass filters for temperature, two bandpass filters for velocity, one Ca II H filter for F-corona, one broadband filter for fast imaging and density, and one neutral density (ND) filter for direct Sun viewing and safety.

• Journal of Mechanical Science and Technology
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• 제16권2호
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• pp.235-245
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• 2002

The present article aims to perform numerical calculations for inter-spray impingement of two diesel sprays under a high injection pressure and to propose a new hybrid model for droplet collision on the basis of literature findings. The hybrid model is compared with the original O'Rourke's model, which has been widely used for spray calculations. The main difference between the hybrid model and the O'Rourke's model is mainly in determination of the collision threshold condition, in which the preferred directional effect of droplets and a critical collision radius are included. The Wave model involving the cavitation effect inside a nozzle is used for predictions of atomization processes. Numerical results are reported for different impingement angles of 60°and 90°in order to show the influence of the impinging angle on spray characteristics and also compared with experimental data. It is found that the hybrid model shows slightly better agreement with experimental data than the O'Rourke's model.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.189-189
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• 2012

Lead sulfide (PbS) nanocrystal quantum dots (NQDs) are promising materials for various optoelectronic devices, especially solar cells, because of their tunability of the optical band-gap controlled by adjusting the diameter of NQDs. PbS is a IV-VI semiconductor enabling infrared-absorption and it can be synthesized using solution process methods. A wide choice of the diameter of PbS NQDs is also a benefit to achieve the quantum confinement regime due to its large Bohr exciton radius (20 nm). To exploit these desirable properties, many research groups have intensively studied to apply for the photovoltaic devices. There are several essential requirements to fabricate the efficient NQDs-based solar cell. First of all, highly confined PbS QDs should be synthesized resulting in a narrow peak with a small full width-half maximum value at the first exciton transition observed in UV-Vis absorbance and photoluminescence spectra. In other words, the size-uniformity of NQDs ought to secure under 5%. Second, PbS NQDs should be assembled carefully in order to enhance the electronic coupling between adjacent NQDs by controlling the inter-QDs distance. Finally, appropriate structure for the photovoltaic device is the key issue to extract the photo-generated carriers from light-absorbing layer in solar cell. In this step, workfunction and Fermi energy difference could be precisely considered for Schottky and hetero junction device, respectively. In this presentation, we introduce the strategy to obtain high performance solar cell fabricated using PbS NQDs below the size of the Bohr radius. The PbS NQDs with various diameters were synthesized using methods established by Hines with a few modifications. PbS NQDs solids were assembled using layer-by-layer spin-coating method. Subsequent ligand-exchange was carried out using 1,2-ethanedithiol (EDT) to reduce inter-NQDs distance. Finally, Schottky junction solar cells were fabricated on ITO-coated glass and 150 nm-thick Al was deposited on the top of PbS NQDs solids as a top electrode using thermal evaporation technique. To evaluate the solar cell performance, current-voltage (I-V) measurement were performed under AM 1.5G solar spectrum at 1 sun intensity. As a result, we could achieve the power conversion efficiency of 3.33% at Schottky junction solar cell. This result indicates that high performance solar cell is successfully fabricated by optimizing the all steps as mentioned above in this work.

• 한국가스학회지
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• 제2권2호
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• pp.1-11
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• 1998

PBL(Poly Butadiene Latex) 반응공정을 연구대상으로 하여 사고 시나리오를 작성하고 시나리오별 정량적 위험성 평가 및 사고결과 영향평가를 실시하였다. 정략적 위험성 평가결과 PBL 반응기가 반응폭주로 인한 사고확률은 $9.197{\times}10^{-5}/yr$로 나타났고, 중요도가 가장 큰 것은 압력방출장치(Relief Device)이다. 사고영향평가 결과 반응기가 폭발이 일어날 때 기준점에서의 최대폭발과압(peak overpressure)은 $5.066{\times}10^5(Pa)$이고, 유리창이 파열될 수 있는 영향(피해) 범위는 거의 공장 전 지역을 포함한다. 폭풍의 직$\cdot$간접적인 원인에 의하여 근로자가 사망할 수 있는 최대 영향반경은 27m이고, 고막의 손상을 일으키기 위한 최대 영향반경은 77m로 나타났다. PBL 반응기가 폭발했을 때 건축물과 같은 구조물이 받을 수 있는 손상 정도는 폭심으로부터 52m까지로 나타났다. 이들 평가 결과를 기준으로 효과적인 안전시설 투자에 대한 시설개선 방향을 제시하였다.

• 한국안전학회지
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• 제23권4호
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• pp.1-6
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• 2008

This experiments are perfol1ned to investigate the effect of ventilation velocity on a high pressure water mist tire suppression in train. The experiment is conducted in half scale modeled train of a steel-welled enclosure (5.0m${\times}$2.4m${\times}$2.2m). The ventilation velocity is controlled by the ventilation duct through an inverter in the range of 0 to 3m/s. The coverage-radius and an injection angle of an high pressure water mist system are measured. The mist nozzle with 5-injection holes is operated with pressure 60bar. The heptane pool fires are used. The fire extinguishment times and the temperature are measured for the ventilation velocities. In conclusion, because the momentum of injected water mist is more dominant than that of ventilation air, the characteristics of water mist, the fire extinguishment times and the temperature are affected very little by ventilation velocity.