• Fibers and Polymers
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• 제1권1호
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• pp.37-44
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• 2000

A finite element method is employed fer a flow analysis of the melt spinning process of a non-circular fiber, a PET(polyethylene terephthalate) filament. The flow field is divided into two regions of die channel and spin-line. A two dimensional analysis is used for the flow within the die channel and a three dimensional analysis fur the flow along the spin-line. The Newtonian fluid is assumed for the PET melt and material properties are considered to be constant except for the viscosity. Effects of gravitation, air drag force, and surface tension are neglected. Although the spin-line length is 4.5 m only five millimeters from the spinneret are evaluated as the domain of the analysis. Isothermal and non-isothermal cases are studied fer the flow within the die channel. The relationship between the mass flow rate and the pressure gradient is presented for the two cases. Three dimensional flow along the spin-line is obtained by assuming isothermal conditions. It is shown that changes in velocity and cross-sectional shape occur mostly in the region of 1mm from the die exit.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 춘계학술발표회논문집(2)
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• pp.36-41
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• 1996

Turbulent thermal mixing experiments by the injection of two parallel non-isothermal water jets have been performed. The turbulent velocities and fluctuations under the isothermal conditions have been measured using LDV system. The velocity vectors have been plotted in two dimensions from the data measured at 29$\times$16 points. The thermal mixing experiments also have been conducted, where we used 45 K-type thermocouples with a sheath diameter of 0.020" which were fixed with 5 mm distance in a line at a measured height. The measured heights were 5, 10, 20, 30, 40 cm from the upper end of rectangular nozzles. We measured the turbulent temperatures under the various flow velocity conditions with 12$^{\circ}C$ $\leq$ $\Delta$T $\leq$4$0^{\circ}C$. The sampling frequency and sampling time were about 420 Hz and 10 seconds, respectively. The measured results of equal velocity parallel jets were analyzed axially and radially to obtain the variation of temperature fluctuation.tion.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 D
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• pp.1569-1571
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• 1999

In this work, we have performed the application experiment for real distribution line to diagnose the underground power cables using DC voltage decay measurement system. We have also performed the Isothermal Relaxation Current test for the same distribution line using KDA-l. We could confirmed possibility of grading the insulation aging state of underground power cables. Therefore, we conclude that it is possible to apply DC voltage decay method to the real distribution line.

• Korean Chemical Engineering Research
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• 제43권2호
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• pp.259-265
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• 2005

Water+n-methylformamide(NMF), benzene+NMF 그리고 toluene+NMF의 353.15 K 이성분계 등온 기-액상평형을 headspace gas chromatography(HSGC)로 측정하였고, NMF+benzene+n-heptane과 NMF+toluene+n-heptane 삼성분계에 대한 298.15 K 액-액상평형을 tie-line 측정법으로 결정하였다. 이성분계 기-액상평형 데이터는 공비점이 없었으며, $g^E$ 모델식(Margules, van Laar, Wilson, NRTL, UNIQUAC)에 비교적 작은 편차로 잘 상관되었다. 삼성분계 tie-line 데이터는 NRTL식과 UNIQUAC식을 이용하여 상관과 추산을 병행하였으며, Hirata-Fujita식과 Maior-Swenson식을 이용하여 정확도를 검증하였다.

• 천문학회보
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• 제33권2호
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• pp.37-37
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• 2008

• 천문학회보
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• 제35권1호
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• pp.28.2-28.2
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• 2010

We have investigated seven Extreme-Ultraviolet (EUV) bright points in the active region (AR 10926) on 2006 December 2 by the EUV imaging spectrometer (EIS) onboard Hinode spacecraft. We determined their Doppler velocities and non-thermal velocities from 15 EUV spectral lines (log T=4.7-7.2) by fitting each line profile to a Gaussian function. We present the Doppler velocity map as a function of temperature which corresponds to a different height. As a result, these active region bright points show two different types of characteristics. Type 1 bright point shows a systematic increase of Doppler velocity from -68 km/s (blue shift) at log T=4.7 to 27 km/s (red shift) at log T=6.7, while type 2 bright points have Doppler velocities in the range of -20 km/s and 20 km/s. Using MDI magnetograms, we found that only type 1 bright point was associated with the canceling magnetic feature at the rate of $2.4{\times}10^{18}$ Mx/hour. When assuming that these bright points are caused by magnetic reconnection and the Doppler shift indicates reconnection out flow, the pattern of the Doppler shift implies that type 1 bright point should be related to low atmosphere magnetic reconnection. We also determined electron densities from line ratio as well as temperatures from emission measure loci using CHIANTI atomic database. The electron densities of all bright points are comparable to typical values of active regions (log Ne=9.9-10.4). For the temperature analysis, the emission loci plots indicate that these bright points should not be isothermal though background is isothermal. The DEM analysis also show that while the background has a single peak distribution (isothermal), the EUV bright points, double peak distributions.

• 한국지리정보학회지
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• 제9권2호
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• pp.227-238
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• 2006

해양에서 수온의 등온선 밀집 정도를 표준지수로 정량화하기 위해 선밀도 지수(line density index: LDI)를 개발하였다. 지수 값의 범위를 0에서 100까지 제한시킨 LDI의 개발과정에 대한 이론적 배경을 기술하였고, line의 총 길이가 해당 면적의 1/10를 넘지 못한다는 적용조건에 대한 타당성 검증도 수행하였다. LDI의 적용 실험을 위해 남해역에서 관측된 NOAA SST 자료를 이용하였다. GIS를 이용하여 SST 레스터 데이터로 부터 $0.1^{\circ}C$ 등온선 벡터 데이터를 선형화하고 단위격자 영역을 폴리곤으로 제작한 후 공간중첩을 통해 LDI를 계산하였다. 단위 영역의 크기가 LDI의 분포에 미치는 영향을 분석하기 위해 두 종류의 격자 크기를 설계하여 LDI의 통계량를 산출하고 정규성 검정을 수행하였다. 분석 결과 격자크기에 따라 LDI의 평균과 정규성 같은 고유특징은 변하지 않으나, 통계량 값의 범위, 분산, 표준편차 등은 변하였는데, 이는 수온전선 구조가 복잡하고 전선폭이 격자 영역보다 훨씬 작을 때 발생하는 문제임이 확인되었다. 또한, LDI와 수온 차(${\Delta}T^{\circ}C$) 와의 관계성을 분석하고 수온전선역의 수온 수평경도(${\Delta}T^{\circ}C/km$)를 선형회귀모델로부터 계산하여 기존 연구자들의 제시한 수온전선역에서의 수온 수평경도 값과도 비교하였다. 본 연구를 통해 새롭게 개발된 LDI가 지니는 의미는 해양환경에서 시 공간적인 변화에 따른 수온전선 형성 지역을 절대적인 지수치로 비교 가능함은 물론, 수온전선과 해양환경 또는 해양생물과의 관계를 정량적으로 분석할 수 있는 기반을 제시했다는 점이다.

• Journal of Welding and Joining
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• 제10권2호
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• pp.19-31
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• 1992

A numerical study was performed to investigate the flow field and the heat transfer characteristics occurring in high power density welding which is important in many fields of engineering applications. A two dimensional quasi-steady state of keyhole welding model is simulated by using the finite volume methods. It is shown that the shape of isothermal line is elliptic and the temperature gradient is very steep compared with other welding method and the welding speed has on welding width and observed beam power.

• Bulletin of the Korean Chemical Society
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• 제8권2호
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• pp.105-110
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• 1987

A theory in which the Enskog hard sphere collisional dynamics complements the hydrodynamic theory is applied to the fast modulation dephasing dynamics in liquids which leads to homogeneous line broadening in the isotropic Raman spectra. The dephasing times of several molecules in pure liquids and in trace solutions in the solvent $CCl_4$ are calculated and these are compared with experimental values. The temperature dependence of the dephasing time of liquid acetonitrile and the isothermal density dependence of the dephasing time of liquid methyl iodide are also investigated.

• 세라미스트
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• 제10권3호
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• pp.67-74
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• 2007

Crystallisation kinetics of the erbium doped soda-tellurite glasses were studied using the differential thermal analysis (DTA) and differential scanning calorimetery (DSC) techniques. The DTA curves in the temperature range of 350 K to 650 K were obtained from isochronal heating rates, chosen in the range of 2 to 20 K/min. DSC isothermal curves were used to calculate the fraction of crystals formed on reheating. The apparent activation energies for devitrification were derived by measuring the shifts in the values of $T_g$ and $T_x$ with heating rates, using the Kissinger method. The derived values of apparent activation energies for isochronal and isothermal methods varied in the range of $190-204\;{\pm}\;5\;kJ\;mol^{-1}$. The X-ray powder diffraction analysis of heat treated and transparent samples showed the presence of nano-scale size sodium-tellurite crystals. These crystallites were found to have a strong influence on the full width of half maxima of the transition in $Er^{3+}:\;^4I_{13/2}{\rightarrow}^4I_{15/2}$, which extended from 70 nm in the vitreous materials to 132 nm in glass-ceramic materials.