• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.17 no.1
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• pp.65-73
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• 1988

Steady laminar natural convection heat transfer from an isothermal square beam with adiabatic wall has been studied for various inclination angles of the wall and Rayleigh numbers by using Mach-Zehnder Interferometer in air. The different temperature and fluid fields were obtained as the inclination angle changes showing the effects of the ascending heated fluid and the adiabatic wall. The maximum total mean Nusselt number was found at ${\theta}=45^{\circ}$.

• Journal of electromagnetic engineering and science
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• v.8 no.1
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• pp.6-11
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• 2008

Advances in low power design open the possibility to harvest energy from the environment to power electronic circuits. Electrical energy can be harvested from piezoelectric transducer. Piezoelectric materials can be used as mechanisms to transfer mechanical energy usually vibrating system into electrical energy that can be stored and used to power other devices. Micro- to milli-watts power can be generated from vibrating system. We developed definitive and analytical models to predict the power generated from a cantilever beam attached with piezoelectric transducer. Analytical models are pin-force method, enhanced pin-force method and Euler-Bernoulli method. Harmonic oscillations and random noise will be the two different forcing functions used to drive each system. It has been selected the best model for generating electric power based upon the analytical results obtained.

• The Transactions of the Korea Information Processing Society
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• v.7 no.3
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• pp.901-908
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• 2000

Satellite communication in the 21 century's high tech information world is developing rapidly, marked by high levels of applications and functions. For example, satellite communication can process and switch the speed of the service provided by a broad and vast digital multimedia system such as a long-distance all between nations or broadcasting transfer service, which is supplied by a contemporary satellite system. So, it bring about problems which lack of satellite orbit and gibes out frequency resource by increment of satellite universally. To support this, an OBP satellite system is need, which includes an on-board IF/RF switch, baseband signal processing, multi-beam antenna technology, as well as a simple transponder system. In this paper, we have outlined the next generation of satellite communication; satellite OBP transport network architecture, which offers multimedia service and applied frequency reuse method for multi-spot beam. The satellite B-ISDN transport network architecture is also analyzed.

• Coupled systems mechanics
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• v.8 no.4
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• pp.289-298
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• 2019

Reinforced concrete can be considered as a heterogeneous material consisting of coarse aggregate, mortar mix and reinforcing bars. This paper presents a two-dimensional mesoscopic analysis of reinforced concrete beams using a simple two-phase mesoscopic model for concrete. The two phases of concrete, coarse aggregate and mortar mix are bonded together with reinforcement bars so that inter force transfer will occur through the material surfaces. Monte Carlo's method is used to generate the random aggregate structure using the constitutive model at mesoscale. The generated models have meshed such that there is no material discontinuity within the elements. The proposed model simulates the load-deflection behavior, crack pattern and ultimate load of reinforced concrete beams reasonably well.

• Imaging Science in Dentistry
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• v.37 no.4
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• pp.205-209
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• 2007

Purpose: To determine the physical properties of a newly developed cone beam computed tomography (CBCT). Materials and Methods: We measured and compared the imaging properties for the indirect-type flat panel detector (FPD) of a new CBCT and the single detector array (SDA) of conventional helical CT (CHCT). Results: First, the modulation transfer function (MTF) of the CBCT were superior to those of the CHCT. Second, the noise power spectrum (NPS) of the CBCT were worse than those of the CHCT. Third, detective quantum efficiency (DQE) of the indirect-type CBCT were worse than those of the CHCT at lower spatial frequencies, but were better at higher spatial frequencies. Although the comparison of contrast-to-noise ratio (CNR) was estimated in the limited range of tube current, CNR of CBCT were worse than those of CHCT. Conclusion: This study shows that the indirect-type FPD system may be useful as a CBCT detector because of high resolution.

• The Korean Journal of Ceramics
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• v.6 no.2
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• pp.129-133
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• 2000

Boron nitride films were synthesized with $N_2$ion flux of low energy, up to 100 eV, at different substrate temperatures of no heating, 200, 400, 500, and $800^{\circ}C$, respectively. Boron was supplied by e-beam evaporation at the rate of $1.5\AA$/sec. For all the conditions, hexagonal BN (h-BN) phase was mainly synthesized and high resolution transmission electron microscopy (HRTEM) showed that (002) planes of h-BN phase were aligned vertical to the Si substrate. The maximum alignment occurred around $400^{\circ}C$. In addition to major h-BN phase, transmission electron diffraction (TED) rings identified the formation of cubic BN (c-BN) phase. But HRTEM showed no distinct and continuous c-BN layer. These results suggest that c-BN phase may form in a scattered form even when h-BN phase is mainly synthesized under small momentum transfer by bombarding ions, which are not reconciled with the macro compressive stress model for the c-BN formation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.11
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• pp.2297-2304
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• 2002

Two-dimensional and three-dimensional finite element methods have been used to analyze the deformation behavior of a shadow mask due to thermal and tension load. The shadow mask inside the Braun tube of a TV set has numerous slits through which the electron beams are guided to land on the designed phosphor of red, green or blue. Its thermal deformation therefore causes landing shift of the electron beam and results in decolorization of a screen. For the realistic finite element analysis, the effective thermal conductivity and the effective elastic modulus arc calculated, and then the shadow mask is modeled as shell without slits. Next a transient thermal analysis of the shadow mask is performed, wherein thermal radiation is a major heat transfer mechanism. Analysis of the resulting thermal deformation is followed, from which the landing shift of the electron beam is obtained. The present finite element scheme may be efficiently used to reduce thermal deformation of a shadow mask and in developing prototypes of a large screen flat TV.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.683-688
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• 2007

Surface heat treatment of SM45C round bar by diode laser was simulated to find it's condition by using commercial finite element code MARC. Due to axisymmetric geometry, a quarter of model for SM45C round bar was considered and user subroutines were applied to boundary condition for the heat transfer. Material properties such as conductivity, specific heat and mass density were given as a function of temperature. Rotation speed of round bar and feed rate of beam were considered to design heat source model. Shape parameter values of heat source were determined by beam profile. As results, Three dimensional heat source model for diode laser beam conditions of surface hardening has been designed by the comparison between the finite element analysis results and experimental data on SM45C round bar. Diode laser surface hardening for SM45C round bar was successfully simulated and it should be useful to determine optimal heat treatment condition.

• Journal of the Korean Vacuum Society
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• v.6 no.4
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• pp.293-297
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• 1997

Using trace etching method in this study, we measure the energy of argon ions generated in VEBA System which is composed of Marx Generater and Pulse Forming Line. In this system the electron beam of 240 kV, 30 kA, 60 ns is generated. Argon ions are formed through the electron beam ionization of a gas cloud injected by a fast puff valve. Thus argon ions are accelerated into vacuum drift tube by a virtual cathode and seperated with electron beam, consequently, they heat the trace etching plates made of aluminum thin films. The energy of argon ions are determined by the number of aluminum thin films penetrated by the ions. This experimental value corresponds with the theoretical value.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1995.11a
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• pp.293-297
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• 1995

In order to investigate the electrical properties of Transformer Oils, Volume Resistivity for transformer oils was made researches. in this paper, the specimen was produced by irradiation of electron beam, which is divided by the dose, 12[Mrad], 24[Mrad], 36[Mrad]. By investigating the electrical properties of dielectric liquid due to the difference of electron beam irradiation the effect of electron beam irradiation was studied. To measure the physcial properties of transformer Oils, Fourier transfer infrared spectroscopy was investigated. And the study for the electrical properties of dielectric liquid was made by measuring volume resistivity of specimen. the Electrode for the measuring Volume resistivity is formed coaxial cylindrical shape, and its geometric capacitance is confirmed to 16[pF]. In this experiments, Highmegohm meter which is model VMG-1000, was used for the measuring volume resistivity. the applying voltages were DC 100, 250, 500, 1000[V] in the temperature range of 20∼120[$^{\circ}C$]. By means of the result from this experiment the movement of carrier and the physcial constants to contribute dielectric properties is introduced.