• The Korean Journal of Rheology
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• v.11 no.1
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• pp.9-17
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• 1999

Viscoelastic characteristics of cured phenolic resin/carbon fiber composite materials were investigated through glass transition and degradation reaction processes in the high temperature region up to $400^{\circ}C$. A typical glass transition of the cross-linked thermoset polymer was followed by irreversible degradation reactions, which were exhibited by the increasing storage modulus and loss modulus peak. A degradation master curve was constructed by using the vertical and horizontal shift factors, both of which complied well with the Arrhenius equation in light of the kinetic expression of degradation rate constants. Using an analogy to the Havriliak-Negami equation in dielectric relaxation phenomena, a viscoelastic modeling methodology was developed to characterize the frequency- and temperature-dependent complex moduli of the degrading thermoset polymer composite systems. The temperature-dependent relaxation time of the degrading composites was determined in a continuous fashion and showed a minimum relaxation time between the glass transition and degradation reaction regions. The capability of the developed modeling methodology was demonstrated by describing the complex behavior of the viscoelastic complex moduli of reacting phenolic resin composite systems.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2009.10a
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• pp.335-338
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• 2009

In this study, in order to investigate the thermal and electrical properties of ZnO arrester block against 60[Hz] AC voltage, the changes in leakage current were measured. The temperature distribution appearing on the ZnO arrester blocks was observed using a forward looking infrared camera. In particular, the correlation between the thermal and electrical properties of a ZnO arrester block was analyzed experimentally. From this analysis, the thermal phenomena resulting from the heat generation and dissipation of the ZnO arrester block were interpreted. The degradation and thermal runaway phenomena of ZnO arrester block are closely related to the temperature limit of the ZnO arrester block. The installation of an additional metal electrode has resulted in the decrease of the leakage current due to the heat dissipation.

• Proceedings of the KIEE Conference
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• 1999.11d
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• pp.994-996
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• 1999

Hygrothermal aging at the elevated temperature induces the long-term degradation of the epoxy resin. We investigated the effects of hydrothermal stress on the dielectric breakdown phenomena of epoxy composite filled with natural zeolite. The cured specimens absorbed the moisture in the autoclave at $120^{\circ}C$. $T_g$ of the deteriorated composite by moisture absorption decreased. The dielectric breakdown strength decreased with the moisture absorption cycle. It was concluded that the thermal stress and the high water-vapour-pressure deteriorated the natural zeolite filled epoxy resin system, consequently and the tree growth rate increased.

• Bulletin of the Korean Space Science Society
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• 2004.10b
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• pp.360-363
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• 2004

This review is concerned with the MP (multipactor) phenomena of the diplexer for RFDU DM of next generation satellite. The MP discharge is serious problems to design RF components in space applications such ase damage of physical structure, performance degradation, and mission failure of the satellite. In this work, we employed the 3D finite element method (FEM) to calculate the critical gap points and adopted ESTEC curve, MP susceptibility zone, to analyze the maximum handling RF power in the diplexer. And this work also recommends that one should design the tx filter of the diplexer which is more wider bandwidth upto the points to escape the ears of the group delay especially the cavity type of RF components in space applications.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.44 no.2
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• pp.222-227
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• 1995

A new IGBT structure, which may suppress latch-up phenomena considerably, is proposed and verified by MEDICI simulation. The proposed structure employing the segmented $n^{+}$ buffer layer increases latch-up current capability due to suppression of the current flowing through the resistance of $p^{-}$ well, $R_{p}$, which is the main cause of latch-up phenomena without degradation of forward characteristics. The length of the $n^{+}$ buffer layer is investigated by considering the trade-off between the latch-up current capability and the forward voltage drop. The segmented $N^{+}$ buffer layer results in better latch-up immunity in comparison with the uniform buffer layer.

• International Journal of Computer Science & Network Security
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• v.22 no.6
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• pp.91-96
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• 2022

The photocatalytic degradation of salicylic acid takes place in several stages involving coupled phenomena, such as the transport of molecules and the chemical reaction. The systems of transport equations and the photocatalytic reaction are numerically solved using COMSOL Mutiphysics (CM) simulation software. CM will make it possible to couple the phenomena of flow, the transport of pollutants (salicylic acid) by convection and diffusion, and the chemical reaction to the catalytic area (bauxite or TiO2 doped by nanoparticles). The simulation of the conversion rate allows to correctly fit the experimental results. The temporal simulation shows that the reaction reaches equilibrium after a transitional stage lasting over one minute. The outcomes of the study highlight the importance of diffusion in the boundary layer and the usefulness of injecting micro-agitation into the microchannel flow. Under such conditions, salicylic acid degrades completely.

• Computers and Concrete
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• v.29 no.1
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• pp.1-14
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• 2022

Several aspects influence corrosive processes in reinforced concrete (RC) structures such as environmental conditions, structural geometry and mechanical properties. Since these aspects present large randomnesses, probabilistic models allow a more accurate description of the corrosive phenomena. Besides, the definition of limit states in the reliability assessment requires a proper mechanical model. In this context, this study proposes a straightforward methodology for the mechanical-probabilistic modelling of RC structures subjected to reinforcements' corrosion. An improved damage approach is proposed to define the limit states for the probabilistic modelling, considering three main degradation phenomena: concrete cracking, rebar yielding and rebar corrosion caused either by chloride or carbonation mechanisms. The stochastic analysis is evaluated by the Monte Carlo simulation method due to the computational efficiency of the Lumped Damage Model for Corrosion (LDMC). The proposed mechanical-probabilistic methodology is implemented in a computational framework and applied to the analysis of a simply supported RC beam and a 2D RC frame. Curves illustrate the probability of failure evolution over a service life of 50 years. Moreover, the proposed model allows drawing the probability of failure map and then identifying the critical failure path for progressive collapse analysis. Collapse path changes caused by the corrosion phenomena are observed.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.33B no.3
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• pp.88-95
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• 1996

Recently, the use of color data is growing fast in the area of image processing. To represent full resolution image on a limited output device, image has to be quantized an dithered. So, many dithering techniques are foundd in the printing. In this paper, we propose nonlinear quantization to consider the overlapping phenomena of neighboring printing dots and modified dot diffusion algorithm to compensate the color degradation produced in the quantization process. In the modified dot-diffusion quantization errors to be diffused are adjusted to improve both image blur and color change produced in the dot diffusion. The printed image obtained by the proposed color dithering method has higher visual quality an less color degradation than the images by conventional printing method.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.40 no.8
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• pp.799-807
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• 1991

The various degradation phenomena, such as the evolution of gases, tan e, moisture content and total acid number in insulation oils of power transformer have been measured and analyzed as a function of aging temperatures and periods. The insulation oils have been degraded at laboratory in the period of 17, 34, and 72 days. We have also extracted the insulation oils from the working power transformers. The dissolved gases (such as CO, CO2, H2, CH4 C2H2---), tane, moisture content and total acid number in laboratory samples and field samples have been measured and characterized. It has been found that gases increase with degradation temperature and tane increases with total acid number while the moisture content does not increase with tane.

• Journal of Welding and Joining
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• v.24 no.2
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• pp.57-63
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• 2006

In this study, the curing kinetics and thermal degradation of underfill were investigated using differential scanning calorimetry (DSC) and thermo gravimetry analysis (TGA). The mechanical and thermal properties of underfill were characterized using dynamic mechanical analysis (DMA) and thermo-mechanical analysis (TMA). Also, we presented on underfill dispensing process using Prostar tool. The non-isothermal DSC scans at various heating rates, the exothermic reaction peak became narrower with increasing the heating rate. The thermal degradation of underfill was composed of two processes, which involved chemical reactions between the degrading polymer and oxygen from the air atmosphere. The results of fluidity phenomena were simulated using Star CD program, the fluidity of the underfills with lower viscosity was faster.