• 천문학회보
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• 제38권2호
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• pp.89.2-89.2
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• 2013

Solar energetic transients, e.g., flares, CMEs, etc., release large amount of energy which is expected to excite acoustic waves (p-modes) by exerting mechanical impulse of the thermal expansion of the flare on the photosphere. We study the p-mode properties of flaring and dormant active regions (ARs) to find association between flare and p-mode parameters. We compute the magnetic and flare activity indices of ARs using the line-of-sight magnetograms and GOES X-ray fluxes, respectively. The p-mode parameters are computed from the ring-diagram analysis. We correct p-mode parameters for magnetic field, filling factors and foreshortening by multiple linear-regression analysis. Our analysis of several flaring and dormant ARs observed during the Carrington rotations 1980-2109, showed strong association of mode parameters with magnetic and flare activities. We find that the mode parameters are contaminated by the geometrical effect. Mode amplitude decreases with angular distance from the solar disc centre. The mode width increases with magnetic activity while amplitude showed opposite relation due to mode absorption by the sunspot. After correcting modes due to all geometrical effects, magnetic activity and filling factor, we find that the modes amplitude, and mode energy increases with flare energy while width shows opposite relation.

• Membrane and Water Treatment
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• 제7권6호
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• pp.477-493
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• 2016

Immediate use of activated carbon incorporated polysulfone membrane application for dye separation was reported in this work. Dimethylformamide (DMF) was used as the solvent for the membrane preparation. The membrane thus prepared were characterized in terms of surface morphology, ATR-FTIR, AFM, experimental results as membrane performance. The resultant nanofiltration (NF) membranes were tested with Congo red dye concentration 200 mg/L. The water permeability was found to be considerably higher than that reported in literature. Experimental results show that the real rejection of the Congo red is 99.57% over the transmembrane pressure 100 psi using 30% activated carbon incorporated membrane. Prepared NF membranes shows the corresponding permeates fluxes were $40Lm^{-2}h^{-1}$ to $82Lm^{-2}h^{-1}$ with different activated carbon percentage incorporated in polysulfone membrane. The present study demonstrated that dye rejection enhanced NF may be a feasible method for the dye wastewater treatment. The overall observations thus indicated that toxic residual dyes can be appreciably separated from the membrane technology, provided that the accompanying polymeric membrane, activated carbon as binding agents and the process parameter levels are astutely selected.

• Nuclear Engineering and Technology
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• 제29권1호
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• pp.35-44
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• 1997

Critical too-Phase flow rates of subcooled water through Short Pipes (L 140039n) with small diameters (D$\leq$7.15 min) have been experimentally investigated for wide ranges of subcooling (0~199$^{\circ}C$) and pressure (0.5~2.0 MPa). To examine the effects of various parameters (i.e., the location of flashing inception, the degree of subcooling, the stagnation temperature and pressure, and the pipe size) on the critical two-phase flow rates of subcooled water through short pipes with small diameters, a total of 135 runs were made for various combinations of test parameters using four different L/D test sections. Experimental results that show effect of various parameters on subcooled critical two phase flow rates are presented in the form of graphs such as the dimensionless mass flux ( $G^{*}$) versus the dimensionless subcooling ( $T_{sub}$$^{*}$) curve. An empirical correlation expressed in terms of a dimensionless subcooling is also obtained for subcooled two-phase flow rates through present test sections. Comparisons between the mass fluxes calculated by present correlation and a total of 755 selected experimental data points of 9 different investigators show that the agreement is fairly good except for very low subcooling data obtained from small L/D (less than 10) orifices.s.s.s.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2012년도 학술발표회
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• pp.38-38
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• 2012

The East Asia (EA) region including China, Taiwan, Japan, and Korea are especially vulnerable to hydrometerological extremes during the boreal summer (June-September). This study, therefore, pursued an exploratory analysis to improve better understanding of the potential impacts of the two types of PJ patterns on WNP Tropical cyclone (TC) activities and TC-induced extreme moisture fluxes over Korea's five major river basins. This study shows that during positive PJ years, the large-scale atmospheric environments are more favorable for the TC activities than those in negative PJ years. During positive PJ year, it is found that there are weaker wind shear, stronger rising motion, as well as large relative humidity over the Korean peninsula (KP) compared to negative PJ years. As a result, TCs making landfall are more exhibited over the southeastern portions of South Korea. Despite the relatively modest sample size, we expect that insights and results presented here will be useful for developing a critical support system for the effective reduction and mitigation of TC-caused disasters, as well as for water supply management in coupled human and natural systems.

• Nuclear Engineering and Technology
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• 제56권1호
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• pp.265-274
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• 2024

The current research focuses on the development of a numerical approach to forecast strongly subcooled flow boiling of FC-72 as the refrigerant in various vertical minichannel shapes for high-heat-flux cooling applications. The simulations are carried out using the Volume of Fluid method with the Lee phase change model, which revealed some inherent flaws in multiphase flows that are primarily due to an insufficient interpretation of shearlift force on bubbles and conjugate heat transfer against the walls. A user-defined function (UDF) is used to provide specific information about this noticeable effect. The influence of shape and the inlet mass fluxes on the flow patterns, heat transfer, and pressure drop characteristics are discussed. The computational results are validated with experimental measurements, where excellent agreements are found that prove the efficiency of the present numerical model. The findings demonstrate that the heat transfer coefficient decreases as the mass flux increases and that the constriction design improves the thermal performance by 24.68% and 10.45% compared to the straight and expansion shapes, respectively. The periodic constriction sections ensure good mixing between the core and near-wall layers. In addition, a slight pressure drop penalty versus the thermal transfer benefits for the two configurations proposed is reported.

• 천문학회보
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• 제41권2호
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• pp.67.3-68
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• 2016

An X1.6 flare occurred in AR 12192 on 2014 October 22 around 14:06 UT and was observed by Hinode, IRIS, SDO and RHESSI. We analyze a bright kernel which produces a white light flare (WLF) with continuum enhancement and a hard X-ray (HXR) peak. Taking advantage of the spectroscopic observations of IRIS and EIS, we measure the temporal variation of the plasma properties in the bright kernel in the chromosphere and corona. We found that explosive evaporation was observed when the WLF occurred, even though the intensity enhancement in hotter lines is quite weak. The temporal correlation of the WLF, HXR peak, and evaporation flows indicates that the WLF was produced by accelerated electrons. To understand the white light emission processes, we calculated the deposited energy flux from the non-thermal electrons observed by RHESSI and compared it to the dissipated energy estimated from the chromospheric lines (Mg II triplet) observed by IRIS. The deposited energy flux from the non-thermal electrons is about $3.1{\times}10^{10}erg\;cm^{-2}s^{-1}$ when we assume a cut-off energy of 20 keV. The estimated energy flux from the temperature changes in the chromosphere measured from the Mg II subordinate line is about $4.6-6.7{\times}10^9erg\;cm^{-2}s^{-1}$, 15 - 22 % of the deposited energy. By comparison of these estimated energy fluxes we conclude that the continuum enhancement was directly produced by the non-thermal electrons.

• Nuclear Engineering and Technology
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• 제44권4호
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• pp.429-436
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• 2012

Critical heat flux (CHF) is the thermal limit of a phenomenon in which a phase change occurs during heating (such as bubbles forming on a metal surface used to heat water), which suddenly decreases the heat transfer efficiency, thus causing localized overheating of the heating surface. The enhancement of CHF can increase the safety margins and allow operation at higher heat fluxes; thus, it can increase the economy. A very interesting characteristic of nanofluids is their ability to significantly enhance the CHF. Nanofluids are nanotechnology-based colloidal dispersions engineered through the stable suspension of nanoparticles. All experiments were performed in round tubes with an inner diameter of 0.01041 m and a length of 0.5 m under low pressure and low flow (LPLF) conditions at a fixed inlet temperature using water, 0.01 vol.% $Al_2O_3$/water nanofluid, and SiC/water nanofluid. It was found that the CHF of the nanofluids was enhanced and the CHF of the SiC/water nanofluid was more enhanced than that of the $Al_2O_3$/water nanofluid.

• 천문학회보
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• 제35권1호
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• pp.30.2-30.2
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• 2010

Numerous operational anomalies and satellite failures have been reported since the beginnings of the "space age". Space weather effects on modern spacecraft systems have been emphasized more and more as increasing their complexity and capability. Energetic particles potentially can destroy and degrade electronic components in satellites. We analyzed the geostationary (GEO) satellite anomalies during 1997-2009 to search possible influences of space weather on the satellite anomalies like power problem, control processor problem, attitude control problem, etc. For this we use particle data from GOES and LANL satellites to investigate space weather effects on the GEO satellites' anomalies depending on Kp index, local time, seasonal variation, and high-energy electron contribution. As results, we obtained following results: (1) there is a good correlation between geomagnetic index(Kp) and anomaly occurrences of the GEO satellite; (2) especially during the solar minimum, occurrence of the satellite anomalies are related to electron flux increase due to high speed solar wind; (3) satellite anomalies occurred more preferentially in the midnight and dawn sector than noon and dusk sector; (4) and the anomalies occurred twice more in Spring and Fall than Summer and Winter; (5) the electron with the lowest energy channel (50-75keV) has the highest correlation (cc=0.758) with the anomalies. High association between the anomalies and the low energy electrons could be understand by the facts that electron fluxes in the spring and fall are stronger than those in the summer and winter, and low-energy electron flux is more concentrated in the dawn sector where the GEO satellite anomalies occurred more frequently than high-energy electron flux. While we could not identify what cause such local time dependences, our results shows that low-energy electrons (~100keV) could be main source of the satellite anomaly, which should be carefully taken into account of operating satellites.

• 한국진공학회지
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• 제14권3호
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• pp.132-137
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• 2005

국내 유일의 연구용 원자로인 하나로에 중성자 반사율 측정장치를 개발 설치하였다. 하나로 중성자 반사율 측정장치는 수직형 시료 배치를 가지며 입사 중성자 빔의 파장은 $2.459\;\AA$이다. 원자로 출력 24 MW에서 금줄방사화법을 이용하여 측정한 단색기 및 시료위치에서의 중성자속은 각각 $4.5\times10^9\;n/cm^2/sec,\;6.64\times10^6\;n/cm^2/sec4이었다. 또한 하나로 중성자 반사율 측정장치를 이용하여 d-PS, $SiO_2$등의 일부 기준 박막 시료에 대하여 반사율을 측정하고 구조 분석을 수행하였다. 장치 성능 평가 결과 장치 최소 반사율은 $\sim10^{-6}$, 측정 가능한 Q 영역은 $0.003\sim0.3\;\AA^{-1}$이었다.

• Journal of Mechanical Science and Technology
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• 제20권12호
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• pp.2218-2229
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• 2006

A conservative finite-volume numerical method for unstructured grids with the cell-centered method has been developed for computing flow and heat transfer by combining the attractive features of the existing pressure-based procedures with the advances made in unstructured grid techniques. This method uses an integral form of governing equations for arbitrary convex polyhedra. Care is taken in the discretization and solution procedure to avoid formulations that are cell-shape-specific. A collocated variable arrangement formulation is developed, i.e. all dependent variables such as pressure and velocity are stored at cell centers. For both convective and diffusive fluxes the forms superior to both accuracy and stability are particularly adopted and formulated through a systematic study on the existing approximation ones. Gradients required for the evaluation of diffusion fluxes and for second-order-accurate convective operators are computed by using a linear reconstruction based on the divergence theorem. Momentum interpolation is used to prevent the pressure checkerboarding and a segregated solution strategy is adopted to minimize the storage requirements with the pressure-velocity coupling by the SIMPLE algorithm. An algebraic solver using iterative preconditioned conjugate gradient method is used for the solution of linearized equations. The flow analysis code (PowerCFD) developed by the present method is evaluated for its application to several 2-D structured-mesh benchmark problems using a variety of unstructured quadrilateral and triangular meshes. The present flow analysis code by using unstructured grids with the cell-centered method clearly demonstrate the same accuracy and robustness as that for a typical structured mesh.