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Search Results: 1 - 10 of 9516 matches for " Jae Park "
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Thermal Radiation, Joule Heating, and Viscous Dissipation Effects on MHD Forced Convection Flow with Uniform Surface Temperature  [PDF]
M. Y. Abdollahzadeh Jamalabadi, Jae Hyun Park
Open Journal of Fluid Dynamics (OJFD) , 2014, DOI: 10.4236/ojfd.2014.42011
Abstract: In this paper, we studied the effects of thermal radiation, Joule heating and viscous dissipation on forced convection flow in a magnetohydrodynamics (namely MHD) pump in rectangular channel with uniform surface temperature. Numerical results were obtained by solving the nonlinear governing momentum and energy equations with steady state fully developed assumptions by finite difference method. The Lorentz force in momentum and Joule heating, and viscous dissipation in energy equation with the Rossel and approximation are assumed to increase the knowledge of the details of the temperature and flow field in order to design a MHD pump. The purpose of this study is the parametric study of a Newtonian fluid in a MHD pump. The values of maximum velocity, fully developed Nusselt number for different values of magnetic density flux, Brinkman number, viscous heating and radiation number are obtained. However, the maximum temperature stays almost constant with magnetic field, as current increases, the velocity and the temperature increase too. Besides, the increase of thermal radiation number causes the increase in effective thermal conductivity and decrease in thermal boundary layer and the Nusselt number at wall.
B_s mixing phase and lepton flavor violation in supersymmetric SU(5)
Park, Jae-hyeon
High Energy Physics - Phenomenology , 2008, DOI: 10.1063/1.3051959;10.1088/1742-6596/171/1/012060
Abstract: The connection between B_s mixing phase and lepton flavor violation is studied in SU(5) GUT. The O(1) phase, preferring a non-vanishing squark mixing, generically implies tau -> (e + mu) gamma and mu -> e gamma. In addition to the facts already well-known, stresses are put on the role of gaugino to scalar mass ratio at the GUT scale and the possible modifications due to Planck-suppressed non-renormalizable operators.
Lepton flavor violation as a probe of squark mixing in supersymmetric SU(5)
Park, Jae-hyeon
High Energy Physics - Phenomenology , 2007,
Abstract: We study flavor violation in a supersymmetric SU(5) grand unification scenario in a model-independent way employing mass insertions. We examine how the quark and the lepton sector observables restrict sfermion mixings. In many cases, a lepton flavor violating process provides a stringent constraint on the flavor structure of right-handed down-type squarks. In particular, mu -> e gamma turns out to be highly susceptible to the 1-3 and 2-3 mixings thereof, due to the radiative correction from the top Yukawa coupling to the scalar mass terms of 10. We also discuss projected sensitivity of forthcoming experiments, and ways to maintain the power of leptonic restrictions even after incorporating a solution to fix the incorrect quark-lepton mass relations.
Long-term and Short-term AC Treeing Breakdown of Epoxy/Micro-Silica/Nano-Silicate Composite in Needle-Plate Electrodes
Jae-Jun Park
Transactions on Electrical and Electronic Materials , 2012,
Abstract: In order to characterize insulation properties of epoxy/micro-silica/nano-silicate composite (EMNC), long-termand short-term AC treeing tests were carried out undr non-uniform electric field generated between needle-plateelectrodes. In a long-term test, a 10 kV (60 Hz) electrical field was applied to the specimen positioned between theelectrodes with a distance of 2.7 mm in an insulating oil bath at 30℃, and a typical branch type electrical tree wasobserved in the neat epoxy resin and breakdown took place at 1,042 min after applying the 10 kVelectrical field.Meanwhile, the spherical tree with the tree length of 237 μm was seen in EMNC-65-0.3 at 52,380 min (36.4 day) andthen the test was stopped because the tree propagation rate was too low. In the short-term test, an electrial field wasapplied to a 3.5 mm-thick specimen at an increasing voltage rate of 0.5 kV/s until breakdown in insulating oil bathat 30℃ and 130℃, and the data was estimated by Weibull statistical analysis. The electrical insulation breakdownstrength for neat epoxy resin was 1,763 kV/mm at 30℃, while that for EMNC-65-0.3 was 2,604 kV/mm, which was amodified value of 47%. As was expected, the breakdown strength decreased at higher test temperatures.
Effect of Amino Silane Coupling Agent on the AC Electrical Breakdown Phenomena of Epoxy/Layered Silicate Nanocomposite in Needle-plate Electrodes
Jae-Jun Park
Transactions on Electrical and Electronic Materials , 2012,
Abstract: The effects of amino silane coupling agent on the AC electrical treeing and breakdown behaviors in an epoxy/layeredsilicate (1 wt%) were examined in needle-plate electrode geometry. A layered silicate was exfoliated in an epoxy baseresin by using our AC electric field apparatus. To measure the tree initiation and propagation and the breakdown rate,an alternating current (AC) of 10 kV (60 Hz) was applied to the specimen in needle-plate electrode arrangement witha 30℃ insulating oil bath. In the epoxy/amino silane system, the tree initiation time was 11.5 times higher and thebreakdown time was 17.9 times higher than those of the neat epoxy resin. The tree initiation time in the epoxy/layeredsilicate (1 wt%) system with the amino silane was 2.0 times higher, and the breakdown time was 1.5 times higher thanthose of the epoxy/layered silicate (1 wt%) system.
Long-term AC Electrical Treeing Behaviors of Epoxy/Layered Silicate Nanocomposites Prepared by a 3-Roll Mill
Jae-Jun Park
Transactions on Electrical and Electronic Materials , 2012,
Abstract: Studies on the effects of layered silicate content on the AC electrical treeing and breakdown behaviors of epoxy/layered silicate nanocomposites were carried out in needle-plate electrode geometry. Wide-angle X-ray diffraction(WAXD) analysis and transmission electron microscopy (TEM) observation showed that 1 wt% of the multilayeredsilicate was fully exfoliated into nano-sized monolayers in the epoxy matrix however, over 3 wt% of the silicate was inan intercalated state. When 1 wt% layered silicates were incorporated, an electrical tree was initiated in 439 min andpropagated at a speed of 2.3 μm/min after applying 781.4 kV/mm, representing a decreased in starting initiation timeby a factor of 11.0 and increase in propagation speed by a factor 8.2 in comparison with neat epoxy resin. These valueswere in great decline after the layered silicate content was increased to 3wt% which implies that the exfoliated silicateblocked the tree initiation and propagation processes effectively. However the effect was largely decreased in theintercalated state.
AC Electrical Breakdown Characteristics of an Epoxy/Mica Composite
Jae-Jun Park
Transactions on Electrical and Electronic Materials , 2012,
Abstract: Epoxy/mica composite was synthesized, in order to use it as an impregnation resin in a vacuum pressureimpregnation (VPI) process, for manufacturing a high voltage rotary machine. The average particle size of the micawas 5~7 μm and its content was 0, 20, 30 and 40 wt%. A plasticizer or a low molecular aliphatic epoxy was also used,to decrease the viscosity of the composite. The AC electrical breakdown strength was estimated in sphere-to-sphereelectrodes, and the electrical breakdown data were estimated by Weibull statistical analysis. The electrical breakdownstrength became higher with the addition of mica; and that of the system with 20 wt% mica was highest. The electricalbreakdown strength of the system with an aliphatic epoxy was higher than that of the system with a plasticizer.
Effect of Silica Particle Size on the Mechanical Properties in an Epoxy/Silica Composite for HV Insulation
Jae-Jun Park
Transactions on Electrical and Electronic Materials , 2012,
Abstract: In order to develop a high voltage insulation material, epoxy/micro-silica composites (EMC) and epoxy/micro-silica/nano-silica composites (EMNC) with three different particle sizes in μm and one particle size in nm were preparedand their tensile and flexural tests were carried out and the data was estimated by Weibull statistical analysis. Thetensile strength of the neat epoxy was 82.8 MPa and those of the EMCs were larger than that of the neat epoxy, andthey were much more advanced by the addition of 10 nm sized nano-silica to the EMCs. Flexural strength showed thesame tendency of the tensile strength. As the micro-particle size decreased, tensile and flexural strength increased.
Cure and Thermal Degradation Kinetics of Epoxy/Organoclay Nanocomposite
Jae-Jun Park
Transactions on Electrical and Electronic Materials , 2012,
Abstract: Epoxy nanocomposite was synthesized through the exfoliation of organoclay in an epoxy matrix, which was composedof diglycidyl ether of bisphenol A (DGEBA), 4,4'-methylene dianiline (MDA) and malononitrile (MN). Organoclay wasprepared by treating the montmorillonite with octadecyl trimethyl ammonium bromide (ODTMA). The exfoliationof the organoclay was estimated by wide angle X-ray diffraction (WAXD) analysis. In order to measure the curerate of DGEBA/MDA (30 phr)/MN (5 phr)/organoclay (3 phr), differential scanning calorimetry (DSC) analysis wasperformed at various heating rates, and the data were interpreted by Kissinger equation. Thermal degradation kineticsof the epoxy nanocomposite were studied by thermogravimetric analysis (TGA), and the data were introduced tothe Ozawa equation. The activation energy for cure reaction was 45.8 kJ/mol, and the activation energy for thermaldegradation was 143 kJ/mol.
Effect of Nanosilica on the Mechanical Properties and AC Electrical Breakdown Strength of Epoxy/Microsilica/Nanosilica Composite
Jae-Jun Park
Transactions on Electrical and Electronic Materials , 2012,
Abstract: Epoxy/microsilica (65 phr)/nanosilica (0~5 phr) composites (EMNC) were prepared in order to develop a high-voltageinsulation material, where phr means parts per hundred relative to the epoxy oligomer. Tensile and flexural tests ofthe composites were carried out, and the AC electrical breakdown strength was measured, after which all the datawere estimated by Weibull statistical analysis. As the nanosilica content increased, the tensile strength increased, andthe highest value was 117.7 MPa in the EMNC system with 3 phr nanosilica, which was ca. 10% higher than that of thesystem without nanosilica. The value then decreased after 3 phr. The flexural strength and AC electrical breakdownstrength showed the same tendencies as the tensile strength. The highest value of the flexural strength was 184.6 MPain the EMNC system with 3 phr of nanosilica, which was ca. 15% higher than that of the system without nanosilica.The strongest value of the AC electrical breakdown strength was 79.0 kV/0.5 mm in the EMNC system with 3 phr ofnanosilica, which was ca. 34% higher than that of the system without nanosilica.
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