• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.5 no.3
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• pp.169-177
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• 1976

The importance of surface conditions of nucleate boiling is well recognized and it has been known that the heat transfer to boiling liquid is closely related to the bubble population density. The bubble population density should depend on various factors such as heat flux, surface roughness, surface contamination, properties of liquid, etc. In this paper the effect of surface conditions on heat transfer in nucleate boiling is treated. The experiments were carried out with distilled water boiler, on the horizontal heating surfaces, sintered with various bronze particle, under atmospheric pressure. In addition, experimental investigation for the polished bronze surface was performed. By studing a coefficient Xb defined by eq. (9), which represents the bubble foaming ability of heating surface, generalized fomula on the heat transfer in the nucleate toiling were expressed. The coefficient $X_b$, determined empirically, is not constant and indicates a major influence of the sintered metal surfaces on the $\Delta$, necessary to sustain nucleate boiling at any given heat flux. In this study, the main results are obtained as follows; (1) At low temperature difference, the coefficient $X_b$ of sintered metal surface was found to he higher than the polished surface throughout the full range of experiments. (2) The optimum sintered structure showing the maximum coefficient $X_b$ has been confirmed to exist and it is encountered when particle diameter is $256{\mu}$.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.90.2-90.2
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• 2012

Geosynchronous electron flux dropouts are most likely due to fast drift loss of the particles to the magnetopause (or equivalently, the "magnetopause shadowing effect"). A possible effect related to the drift loss is the radial diffusion of PSD due to gradient of PSD set by the drift loss effect at an outer L region. This possibly implies that the drift loss can affect the flux levels even inside the trapping boundary. We recently investigated the details of such diffusion process by solving the diffusion equation with a set of initial and boundary conditions set by the drift loss. Motivated by the simulation work, we have examined observationally the energy spectrum and pitch angle distribution near trapping boundary during the geosynchronous flux dropouts. For this work, we have first identified a list of geosynchronous flux dropout events for 2007-2010 from GOES satellite electron measurements and solar wind pressures observed by ACE satellite. We have then used the electron data from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft measurements to investigate the particle fluxes. The five THEMIS spacecraft sufficiently cover the inner magnetospheric regions near the equatorial plane and thus provide us with data of much higher spatial resolution. In this paper, we report the results of our investigations on the energy spectrum and pitch angle distribution near trapping boundary during the geosynchronous flux dropout events and discuss implications on the effects of the drift loss on the flux levels at inner L regions.

• Bulletin of the Korean Space Science Society
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• 2011.04a
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• pp.28.2-28.2
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• 2011

Coronal Mass Ejections (CMEs) are enormous eruptions of plasma ejected from the Sun into interplanetary space, and mainly responsible for geomagnetic storms and solar energetic particle events. It is very important to infer their direction of propagation, speed and their 3-dimensional configurations in terms of space weather forecast. Two STEREO satellites provide us with 3-dimensional stereoscopic measurements. Using the STEREO observations, we can determine the 3-dimensional structure and radial velocity of the CME. In this study, we applied three different methods to the 2008 April 26 event: (1) Ice cream Cone Model by Xue (2005) using the SOHO/LASCO data, (2) Flux rope model by Thernisien (2009) using the STEREO/SECCHI data, (3) Flux rope model with zero angle using the STEREO/SECCHI data. The last method in which separation angle of flux rope is zero, is similar to the ice cream cone model morphologically. The comparison shows that the radial speeds from three methods are estimated to be about 750km/s and are within ${\pm}120km/s$. We will extend this comparison to other CMEs observed by STEREO and SOHO/LASCO.

• Bulletin of the Korean Space Science Society
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• 2008.10a
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• pp.25.2-25.2
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• 2008

Polar rain is a spatially uniform precipitation of electrons with energies around 100eV that penetrate into the polar cap region where geomagnetic field lines are connected to the Interplanetary Magnetic Fields (IMF). Since their occurrences depend on the IMF sector polarity, they are believed to originate from the field aligned component of the solar wind. However, statistically direct correlation between polar rain and solar wind has not been shown. In this presentation, we examined specifically the IMF strength influence on the polar rain flux variation by classifying of IMF sector polarities. For this study, we employed the polar rain flux data measured by STSAT-1 and compared them with the solar wind parameters obtained from the WIND and ACE satellites. We found the direct mutuality between polar rain flux and IMF strength with correlation coefficient above 0.5. This proportional tendency appears stronger when the northern hemisphere is in the away sector of the IMF, which could be associated with a favorable geometry for magnetic reconnection. Simple particle trajectory simulation clearly shows why polar rain intensity depends on the IMF sector polarity. These results are consistent with the direct entry model of Fairfield et al.(1985), while low correlation coefficient with solar wind density, the similarity between slops of both energy spectra shows that transport process occur without acceleration.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.82.3-83
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• 2017

We investigate the relationships between the peak fluxes of 18 solar energetic particle (SEP) events and associated coronal mass ejection (CME) 3D parameters (speed, angular width, and separation angle) obtained from SOHO, STEREO-A and/or B for the period from 2010 August to 2013 June. We apply the STEREO CME Analysis Tool (StereoCAT) to the SEP-associated CMEs to obtain 3D speeds and 3D angular widths. The separation angles are determined as the longitudinal angle between flaring regions and magnetic footpoints of the spacecraft, which are calculated by the assumption of Parker spiral field. The main results are as follows. 1) We find that the dependence of the SEP peak fluxes on CME 3D speed from multi-spacecraft is similar to that on 2D CME speed. 2) There is a positive correlation between SEP peak flux and 3D angular width from multi-spacecraft, which is much more evident than the relationship between SEP peak flux and 2D angular width. 3) There is a noticeable anti-correlation (r=-0.62) between SEP peak flux and separation angle. 4) The multiple regression method between SEP peak fluxes and CME parameters shows that the longitudinal separation angle is the most important parameter, and the CME 3D speed is secondary on SEP peak flux.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.1
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• pp.95-98
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• 2013

Plate thermometers are used for measuring the radiative heat flux in high-temperature surroundings. The heat flux is calculated from the temperature measured at the back surface of the stainless steel surface of the meter. Heat fluxes from a Schmidt-Boelter gauge are measured as reference heat fluxes. A combined conductive coefficient is introduced to consider the heat loss to insulation, conduction through the stainless plate depth, and conduction from the non-uniform temperature of the plate of the plate thermometer. This coefficient is obtained using the repulsive particle swarm optimization.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.106-109
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• 2007

The spray plume characteristics of liquid water jet injected into subsonic cross-flow at 42 m/s were experimentally investigated. Nozzle has a 1.0 m diameter and L/D=5. Droplet sizes, velocities, volume flux were measured at each downstream area of the injector exit using phase Doppler particle anemometry. Measuring probe position is moved with 3-way transversing machine. Experimental results indicate that SMD is varied from 75 to $120{\mu}m$ distribution and it is uncertain layer structure. SMD peaks at the top of the spray plume. This phenomenon is related to the momentum exchange between column waves and cross-flow stream. Droplet vector velocities were varied from 11.5 to 33 m/s. A higher-velocity region can be identified in down edge region at Z/D : 40, 70 and 100. Lower-velocity region were observed on bottom position of the spray plume. Volume flux is a criterion to the droplet concentration. All volume flux distribution has a same structure that continuously decreases from the center region to the edge of the plume. Z/D : 20 is spatially less concentrated than in Z/D : 100.

• Bulletin of the Korean Chemical Society
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• v.28 no.9
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• pp.1467-1471
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• 2007

The green-emitting CeMgAl11O19:Tb (CMAT) phosphor has been prepared at 1200 °C by the simple solid-state reaction using AlF3 as a self-flux. This preparation temperature is much lower than those (1500-1700 °C) for conventional solid-state reaction and spray pyrolysis method. In particular, the complete process to produce high-quality phosphor particles was carried out through the single-step heat treatment of the mixture of corresponding oxide-type metal sources. An addition of AlF3 as a self-flux significantly decreased the crystallization temperature of CMAT with plate-like shape. The particle morphology could be controlled from plate-like to spherical by using H3BO3 as an additional flux. Thus, an optimal morphology and luminescence characteristics of CMAT were achieved when both AlF3 and H3BO3 fluxes were simultaneously used. Compared with conventional solid-state process, which is accompanied by the calcination step(s), and other alternative liquid solution techniques such as sol-gel method and spray pyrolysis, no use of active precursors and liquid media that are harmful to the environment is a distinctive advantage for the industrial purpose.

• Nuclear Engineering and Technology
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• v.49 no.4
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• pp.787-791
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• 2017

Americium-beryllium (Am-Be; n, ${\gamma}$) is a neutron emitting source used in various research fields such as chemistry, physics, geology, archaeology, medicine, and environmental monitoring, as well as in the forensic sciences. It is a mobile source of neutron activity (20 Ci), yielding a small thermal neutron flux that is water moderated. The aim of this study is to develop a model to increase the neutron thermal flux of a source such as Am-Be. This study achieved multiple advantageous results: primarily, it will help us perform neutron activation analysis. Next, it will give us the opportunity to produce radio-elements with short half-lives. Am-Be single and multisource (5 sources) experiments were performed within an irradiation facility with a paraffin moderator. The resulting models mainly increase the thermal neutron flux compared to the traditional method with water moderator.

• Membrane Journal
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• v.8 no.2
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• pp.102-108
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• 1998

Permeation behavior of the semiconductor rinsing wastewater containing Si particles was examined by ultrafiltration using the polysulfone plate membrane. The permeation flux was gradually decreased with time. It was due to the growth of cake deposited on the membrane surface and the pore plugging by Si particles. Permeation flux of cross flow type was 1.4 times higher than that of the dead end flow type. Nitrogen back flushing which is the removing method of membrane fouling was superior to the water sweeping. With nitrogen back flushing, the decrease of permeation flux due to the fouling was recovered about 85 % to the initial flux in the flat plate membrane system. The rejection rate of Si particles was about 90 % and the size of Si particle in the permeate was about 70 nm.