• Fire Science and Engineering
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• v.11 no.2
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• pp.19-24
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• 1997

numerical simulation of unsteady heat conduction equation were carried out by finite control volume method using the gas temperature derived from fire model as a boundary value. The reduction of compressive and flexural by heating were calculated from the temperature and the given reduction rate. It is shown that this method could be well applied to assess the safety of concrete column or beam of the burned building.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.955-959
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• 2004

The effects of conduction band offset on 2 dimensional electron gas (2DEG) in N-InAlAs(AlAsSb)/InGaAs/InAlAs (AlAsSb) metamorphic heterostructures (MMHS) are studied. A combination of the Shubnikov-deHaas oscillations and the Hall measurements is used to investigate the electron transport properties of these structures. The mobility in the second subband is higher than that in the first subband in all heterostructures. This is attributed to the fact that electrons in the first subband we, on average, closer to the interface and are therefore scattered more strongly by ionized impurities. The results suggest that intersubband scattering rate is more dominant in structures with higher conduction band offset whereas alloy scattering is found to be more dominant in the higher band offset system.

• Journal of the Korean Institute of Telematics and Electronics
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• v.24 no.3
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• pp.445-452
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• 1987

In this paper, a model for characteristics in the AlxGa1-xAs layer of MODFET's is presented. The characteristics of conduction band in the AlxGa1-xAs layer is analyzed with the Fermi-Dirac statistics. And using the conduction band energy which is calculated with the numerical calculation method (false-Positon method), the variations of the electric-field distribution, the ionized donor concentration, and the two-dimensional electron gas density with gate voltage are calculated, respectively. The channel formation process for the parasitic MESFET operation in the MOD structure is also analyzed, and the characteristics in the AlxGa1-xAs layer is analytically modeled. The throretical results describe well the general characteristics in the MOD structure.

• Journal of the Korean Ceramic Society
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• v.54 no.5
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• pp.366-379
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• 2017

Nanostructured materials have attracted considerable research interest over the recent decades because of their potential applications in nanoengineering and nanotechnology. On the other hand, the developments in nanotechnology are strongly dependent on the availability of new materials with novel and engineered morphologies. Among the novel nanomaterials reported thus far, composite nanofibers (NFs) have attracted considerable attention in recent years. In particular, metal oxide NFs have great potential for the development of gas sensors. Highly sensitive and selective gas sensors can be developed by using composite NFs owing to their large surface area and abundance of grain boundaries. In composite NFs, gas sensing properties can be enhanced greatly by tailoring the conduction channel and surface properties by compositional modifications using the synergistic effects of different materials and forming heterointerfaces. This review focuses on the gas sensing properties of composite NFs synthesized by an electrospinning (ES) method. The synthesis of the composite NFs by the ES method and the sensing mechanisms involved in different types of composite NFs are presented along with the future perspectives of composite NFs.

• Journal of Electrical Engineering and Technology
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• v.4 no.4
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• pp.510-514
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• 2009

This paper presents the coupled analysis method to calculate the temperature rise in a gas insulated busbar (GIB). Harmonic eddy current analysis is carried out and the power losses are calculated in the conductor and enclosure tank. Two methods are presented to analyze the temperature distribution in the conductor and tank. One is to solve the thermal conduction problem with the equivalent natural convection coefficient and is applied to a single phase GIB. The other is to employ the computational fluid dynamics (CFD) tool which directly solves the thermal-fluid equations and is applied to a three-phase GIB. The accuracy of both methods is verified by the comparison of the measured and calculated temperature in a single phase and three-phase GIB.

• Transactions of the Korean Society of Automotive Engineers
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• v.5 no.4
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• pp.179-189
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• 1997

Among aftertreatment devices which reduce exhaust gas of diesel engine, diesel oxidation catalyst(DOC) with high reduction efficiency for gaseous matter and particulate matter is now studied actively. In this study, a transient one-dimensional model developed to simulate the thermal and conversion characteristics of adiabatic monolithic converters operating under warm up conditions is presented. This model takes into account the gas solid heat and mass transfer, axial heat conduction, chemical reactions and the related heat release. The model has been used to analyze the transient response of an axisymmetric catalytic converter during a warm-up as a function of catalyst design parameters and operation conditions in order to observe their effects on the lightoff behaviour. The experimental test was carried out 2400 cc light diesel engine with DOC.

• 한국연소학회:학술대회논문집
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• 2012.11a
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• pp.49-51
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• 2012

In this paper, the integration issue, such as an air-side integration design between the gas turbine and air separation unit, is described and analyzed by the exergy and energy balance of the combined-cycle power block in an IGCC power plant. The results showed that the net power of the system was almost same, but that of the gas turbine was decreased as the integration degree increased. The highest exergy loss was occurred in the combustor of gas turbine, which was affected by the chemical reaction, heat conduction, mass diffusion, and viscous dissipation.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.309-309
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• 2000

The main objective of this study is to understand the regeneration step of the PTSA(Pressure and thermal swing adsorption) process below the atmospheric pressure by rigorous dynamic simulation. This target process is to recover toluene using activated carbon as an adsorbent. To do this, the dynamic simulations for the regeneration step are performed at 360, 490, 590mmHg and at high temperature after the simulation of the adsorption step at latm and 298K. A mathematical model was developed to simulate the column dynamics of the adsorption systems. This model is based on non-equilibrium, non-isothermal and non-adiabatic conditions, and axial dispersion and heat conduction are also considered. Heat transfer resistances are considered in gas-solid, gas-column wall and column wall-outside air. The LDF(Linear Driving Force) approximation model describes the mass transfer rate between the gas and solid phase. This study shows that the recovery of toluene by PTSA is more preferable than that by general TSA.

• Journal of Korean Vacuum Science & Technology
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• v.1 no.1
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• pp.19-23
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• 1997

The conductance of a microscopic constriction in a two-dimensional electron gas is obtained as a function of both the constriction width and curvature. When the quantized conductance G at plateaus is given by the channel number Nc times the quantum unit 2e2/h, Nc is found to be a function of not only the width and but also the curvature. At a given W, Nc increases by one whenever the constriction curvature decreases by about a certain value. Until the shape smoothness becomes comparable to the two parallel boundaries, there exist more channels avaliable for conduction in a smaller-curvature constriction than in a larger-curvature one. This result is very interesting because Nc has been considered to depend on the width W only. this reflects that the number of the quantized transverse levels depend o both the constriction width and curvature in a two-dimensional electron gas.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.29A no.3
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• pp.59-65
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• 1992

In this paper, the Numerov method is applied to solve the Schroedinger equation for $Al_{0.3}Ga_{0.7}AS/GaAs/Al_{0.3}Ga_{0.7}As$ double-heterojunction HEMT structures. The 3 subband energy levels, corresponding wave functions, 2-dimensional electron gas density, and conduction band edge profile are calculated from a self-consistent iterative solution of the Schroedinger equation and the Poisson equation. In addition, 2-dimensional electron gas densities in a quantum well of double heterostructure are calculated as a function of applied gate voltage. The density in the double heterojunction quantum well is increased to about more than 90%, however, the transconductance of the double heterostructure HEMT is not improved compared to that of the single heterostructure HEMT. Thus, double-heterojunction structures are expected to be suitable to increase the current capability in a HEMT device or a power HEMT structure.