• Journal of Astronomy and Space Sciences
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• v.28 no.4
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• pp.253-260
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• 2011

To reproduce the multiple broad peaks and the fine spectral features in the spectral energy distributions (SEDs) of T Tauri stars, we model dust around T Tauri stars using a radiative transfer model for multiple isothermal circumstellar dust shells. We calculate the radiative transfer model SEDs for multiple dust shells using the opacity functions for various dust grains at different temperatures. For six sample stars, we compare the model results with the observed SEDs including the Spitzer spectral data. We present model parameters for the best fit model SEDs that would be helpful to understand the overall structure of dust envelopes around classical T Tauri stars. We find that at least three separate dust components are required to reproduce the observed SEDs. For all the sample stars, an innermost hot (250-550 K) dust component of amorphous (silicate and carbon) and crystalline (corundum for all objects and forsterite for some objects) grains is needed. Crystalline forsterite grains can reproduce many fine spectral features of the sample stars. We find that crystalline forsterite grains exist in cold regions (80-100 K) as well as in hot inner shells.

• Journal of Welding and Joining
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• v.25 no.2
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• pp.62-69
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• 2007

A kinetic model fur the particle coarsening behavior was developed. The proposed model considered the critical particle size which can be derived from Gibbs-Thomson equation unlike the conventional approach. In this study, the proposed particle coarsening model was applied to study the coarsening behavior of titanium nitride (TiN particle) in microalloyed steel weld HAZ. Particle size distributions and mean particle size by the proposed model were in agreement with the experimental results. Meanwhile, using additivity rule, the isothermal model was extended to predict particle coarsening behavior during continuous thermal cycle.

• Journal of Welding and Joining
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• v.24 no.1
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• pp.77-87
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• 2006

Considering ferrite grain size in the base metal, the prediction model for $A_{c3}$ temperature and prior austenite grain size at just above $A_{c3}$ temperature was proposed. In order to predict $A_{c3}$ temperature, the Avrami equation was modified with the variation of ferrite grain size, and its kinetic parameters were measured from non-isothermal data during continuous heating. From calculation using a proposed model, $A_{c3}$ temperatures increased with increasing ferrite grain size and heating rate. Meanwhile, by converting the phase transformation kinetic model that predicts the ferrite grain size from austenite grain size during cooling, a prediction model for prior austenite grain size at just above the $A_{c3}$ temperature during heating was developed.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.1
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• pp.204-208
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• 2000

An approximate similarity theory has been applied to predict the forming load of non-axisymmetric forging of aluminum alloys through model material tests. The approximate similarity theory is applicable when strain rate sensitivity, geometrical size, and die velocity of model materials are different from those of real materials. Actually, the forming load of yoke, which is an automobile part made of aluminum alloys(Al-6061), is predicted by using this approximate similarity theory. Firstly, upset forging tests are have been carried out to determine the flow curves of three model materials and aluminum alloy(Al-6061), and a suitable model material is selected for model material test of Al-6061. And then hot forging tests of aluminum yokes have been performed to verify the forming load predicted from the model material, which has been selected from above upset forging tests. The forming loads of aluminum yoke forging predicted by this approximate similarity theory are in good agreement with the experimental results of Al-6061 and the results of finite element analysis using DEFORM-3D.

• Journal of the Korean Society for Heat Treatment
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• v.31 no.4
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• pp.180-186
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• 2018

High temperature flow behaviors of Fe-Cr-Mo-V-W-C tool steel were investigated using isothermal compression tests on a Gleeble simulator. The compressive test temperature was varied from 850 to $1,150^{\circ}C$ with the strain rate ranges of 0.05 and $10s^{-1}$. The maximum height reduction was 45%. The dynamic softening related to the dynamic recrystallization was observed during hot deformation. The constitutive model based on Arrhenius-typed equation with the Zener-Hollomon parameter was proposed to simulate the hot deformation behavior of Fe-Cr-Mo-V-W-C steel. An artificial neural network (ANN) model was also developed to compare with the constitutive model. It was concluded that the ANN model showed more accurate prediction compared with the constitutive model for describing the hot compressive behavior of Fe-Cr-Mo-V-W-C steel.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.43 no.5 s.311
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• pp.60-67
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• 2006

Thermal analysis and prediction of electronic components is required to predict and optimize the reliability of onboard electronic unit employed in space vehicles. This paper introduces a methodology on thermal prediction that uses isothermal PCB model, thermal force model, thermal resistance matrix and superposition principle to calculate electronic devices temperatures undergoing thermal conduction environment. An example is Presented including a prediction result by this method and simulation results performed by commercial program.

• Korea-Australia Rheology Journal
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• v.12 no.2
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• pp.119-124
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• 2000

Employing the Phan-Thien tanner (PTT) fluids model, dynamic behavior of the non-isothermal melt spinning has been investigated. Subjects such as draw resonance instability, the effects of spinline cooling and of the fluid viscoelasticity on the spinning dynamics have been studied using the governing equations of the system. In particular, the draw resonance criterion based on the traveling times of various kinematic waves in the spinline has been confirmed, the reason why the spinline cooling is stabilizing is analyzed, and the effect of fluid viscoelasticity on the spinline stability is summarized. It is believed that the same method as in this study can be applied with equal ease to other extension deformation processes like film casting and film blowing.

• Korean Journal of Materials Research
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• v.9 no.1
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• pp.99-103
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• 1999

We investigated the crystalline behavior in active ion implanted silicon through Raman spectroscopy. Four a-Si(amorphous Si) peaks were observed that are related to the ion implantation induced a-Si layer. After the isochronical anneal(30min). and isothermal anneal($450^{\circ}C$), noticeable recovery of crystalline-Si peak at 519cm\ulcorner and peak center shift of the a-Si TO from 465cm\ulcorner to 480cm\ulcorner were observed by RNM(Random Network Model). By applying RNM and SCLM(Spatial Correlation Length Model), the peak center and FWHM(the Full Width at half Maximum) of a-Si were changed dramatically between T\ulcorner=$200^{\circ}C$ and 30$0^{\circ}C$. From the results, it can be said that there is an abrupt structural change at this temperature region.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.762-767
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• 2007

As a macromolecule material, melted rubber flow shows characteristics of shear thinning fluid. The dynamic viscosity of this rubber fluid is influenced by temperature and shear strain rate. In this study, the numerical simulation of rubber extrusion forming process has been performed using commercial CFD code, Polyflow. Power-law model considering the effect of shear rate is used for the computer simulation of this non-Newyonian flow. Also Non-isothermal behavior is considered as Arrhenius-law model. Distributions of velocity and temperature are predicted through the simulation.

• Journal of the Korean Society of Safety
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• v.13 no.4
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• pp.192-198
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• 1998

MRSM(modified response surface methodology)-2 model is presented for the prediction of boiling points in combustible solution of quaternary systems. This model requires only normal boiling points of pure substances and group-group parameters which are based on the group-group concepts without the use of experimental data under consideration. By means of this methodology, it is possible to predict the boiling points of the combustible mixture of quaternary systems by plotting of isothermal lines using computer graphics. The proposed methodology has been tested and compared successfully with reported boiling points in journals for the combustible solution of quaternary systems. It is hoped eventually that this methodology will permit prediction of the flash point and flammability limit for the combustible mixture of multicomponent systems.