• Journal of the Korean Solar Energy Society
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• v.34 no.1
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• pp.48-57
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• 2014

The transient and synchronization behaviors of a TA (thermo acoustic) laser pair were investigated experimentally for various crossing angles and different separation distances between the laser openings. Sound waves generated by the lasers were measured and analyzed at or near the focusing point by means of microphones, SPL meters, and a commercial software called Signal-Express. The two TA lasers were acoustically coupled through the air mass between their openings, and the only mode-locking operation that could be achieved was the one that was nearly $180^{\circ}C$ out of phase. The time to achieve synchronization was found to be dependent upon the initial mistuning of the frequencies and the crossing angle between the laser axes. The synchronization process could also be accelerated by turning on the laser with the lower power input first.

• Journal of the Korean Magnetics Society
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• v.2 no.1
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• pp.50-55
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• 1992

Numerical method for analyzing the reading process in magnetic recording system is described. Hysteresis characteristics must be included in numerical analysis not only recording process but also reading process because of hysteretic behavior of recording media. Algorithm which is consisted of finite clement method for numerical analysis and Preisach model considered to be more appropriate method than Stoner-Wohlfarth model with spin curling mode for describing hysteresis characteristics is constructed. Equations to calculate waveform of reproduced voltage is proposed. Then, this is applied to perpendicular magnetic recording systems with pole type head and double layer media. Waveform of magnetic flux density and reproduced voltage induced in head coil is obtained. If the recording current increase in recording process, magnitude of reproduced voltage in reproducing process saturates. From this saturation curve, value of current which produce maximum voltage can be obtained.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.285-287
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• 2005

During fabrication of deck house block in passenger ships, the problem of unexpected large deformation and distortion frequently occurs. In this case, line and spot heating method were widely used to correct the distortion of thin plate structure. Spot heating was especially used for the case under 5mm thickness. Few papers are available on the working conditions of spot heating method but only little information on deformation control. In this study, evaluation was carried out on the temperature distribution of spot heating methods using FEA and practical experiments for various heating time. IIn FEA, heat input model was established using Tsuji's double Gaussian heat input mode (Tsuji, I., 1988). This model was verified by comparing with experimental data. Also radial shrinkage and angular distortion due to spot heating were determined and compared with experimental results. Thermo elasto-plastic analysis was performed using commercial FE code, MSC/MARC. Radial shrinkage and angular distortion were measured using 3D measuring apparatus. Based on these results, simplified analysis model for deformation by spot heating was established.

• Journal of Korean Society of Water and Wastewater
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• v.29 no.3
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• pp.427-436
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• 2015

Developing two process models to simulate wastewater treatment process is needed to draw a comparison between measured BOD data and estimated process model data: a mathematical model based on the process mass-balance and an ANN (artificial neural network) model. Those two types of simulator can fit well in terms of effluent BOD data, which models are formulated based on the distinctive five parameters: influent flow rate, effluent flow rate, influent BOD concentration, biomass concentration, and returned sludge percentage. The structuralized mass-balance model and ANN modeI with seasonal periods can estimate data set more precisely, and changing optimization algorithm for the penalty could be a useful option to tune up the process behavior estimations. An complex model such as ANN model coupled with mass-balance equation will be required to simulate process dynamics more accurately.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.1
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• pp.36-43
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• 1988

A two phase model for the simulation of flame propagation has been developed and applied to a mixture of coal air. The effects associated with changes in the initial coal partial equivalence ratio and the initial diameter of particles on the structure of laminar flame propagation have been studied qualitatively and quantitatively. Especially the flame structure, the burning velocity, and the thermal behavior were evaluated. It was found that the radiative heat transfer absolutely dominates over the conduction mode. The increase in particle size was seen to contribute to an obvious increase in burning velocity for fuel lean and stoichiometric mixture. But for fuel rich mixture, the burning velocity was found to exhibit a weaker dependence on particle size.

• Korean Journal of Human Ecology
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• v.24 no.5
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• pp.701-712
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• 2015

This study analyses "Survey of Health and Behavior of Children and Adolescents" which is conducted by National Youth Policy Institute that investigated influential factors in difference between actual obesity and perceptional obesity. GLM (Generalized Linear Mode) was carried out to estimate the effects on the eating habits and physical activities and multinomial logit analysis was carried out to examine the influential factors in difference between actual, obesity and perceptional obesity. The results of this study are shown as follows. First 72.0% of total respondents showed the congruence between actual obesity and perceptional obesity and 24.6% of total respondents perceived them fatter than actual. The remaining 3.5% perceived them thinner than actual. Second, the main effects of actual obesity and perceptional obesity on eating habits were statistically significant, but interaction effect between them was not statistically significant. The main effects of actual obesity and perceptional obesity on physical activities and interaction effect between them were all statistically significant. Third, the influential factors in difference between actual obesity and perceptional obesity were gender, age, school record, education of parents, subjective economic status, and living together with family.

• Journal of Powder Materials
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• v.10 no.3
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• pp.195-200
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• 2003

Ni coated $Al_2O_3$ composite was successfully Prepared by the electroless deposition Process. The average size of Ni particles coated on the $Al_2O_3$ matrix powder was about 20 nm. It was hard to find any reaction compound as an impurity at interface between $Al_2O_3$ and Ni particles after sintering. The characterization of microstructure crystal structure and fracture behavior of the sintered body were investigated using XRD, TEM and Victors hardness tester, and compared with those of the sintered $Al_2O_3$ monolithic body. Many dislocations were observed in the Ni phase due to the difference of thermal expansion coefficient between $Al_2O_3$ and Ni phase, and no observed microcracks at their $Al_2O_3$ and Ni interface. In the $Al_2O_3$/Ni composite, the main fracture mode showed a mixed fracture with intergranular and transgranuluar type having some ,surface roughness. The fracture toughness was slightly increased due to the plastic deformation mechanism of Ni phase in the $Al_2O_3$/Ni composite.

• Journal of Surface Science and Engineering
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• v.46 no.1
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• pp.42-47
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• 2013

The strain-induced phase transformation from austenite to martensite is responsible for the high strength and ductility of TRIP steels. However high strength steels are susceptible to hydrogen embrittlement. This study aimed to evaluate the effects of hydrogen on the behavior of hydrogen delayed fracture in TRIP steel with hydrogen charging conditions. The electrochemical hydrogen charging was conducted at each specimen with varying current density and charging time. The relationship between hydrogen concentration and mechanical properties of TRIP steel was established by SP test and SEM fractography. The maximum loads and displacements of the TRIP steel in SP test decreased with increasing hydrogen charging time. The results of SEM fractography investigation revealed typical brittle mode of failure. Thus it was concluded that hydrogen delayed fracture in TRIP steel result from the diffusion of hydrogen through the ${\alpha}$' phase.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.10 no.4
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• pp.55-64
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• 2011

This study aims to analyze of the impact of converged information with tourism and Bus Information on recreational bus travel. The research has conducted as the following process : A survey was implemented that the user preference behavior as if they were provided a converged information with tourism and bus information on bus usage. As a result, we found that able to using mobile media, having a experience visiting the tourism site, evaluate willingness to pay of the information highly, the 20s age, increasing income variables are concerned with positive relation, and the factors which are using the main mode by auto and having a auto are negative relation on bus usage actively.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.1
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• pp.51-56
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• 2012

The resonance properties of circular vertical-cavity surface-emitting lasers (VCSELs) are studied by using a newly developed equivalent network approach. Optical parameters, such as the stop-band or the reflectivity of periodic Bragg mirrors and the resonance wavelength, are explored for the design of these structures. To evaluate the differential quantum efficiency and the threshold current density, a transverse resonance condition of circular modal transmission-line theory is also utilized. This approach dramatically reduces the computational time as well as gives an explicit insight to explore the optical characteristics of circular VCSELs.