• Steel and Composite Structures
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• v.41 no.6
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• pp.821-829
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• 2021

Nonlinear dynamic response of a sandwich beam considering porous core and nano-composite face sheet on nonlinear viscoelastic foundation with temperature-variable material properties is investigated in this research. The Hamilton's principle and beam theory are used to drive the equations of motion. The nonlinear differential equations of sandwich beam respect to time are obtained to solve nonlinear differential equations by Homotopy perturbation method (HPM). The effects of various parameters such as linear and nonlinear damping coefficient, linear and nonlinear spring constant, shear constant of Pasternak type for elastic foundation, temperature variation, volume fraction of carbon nanotube, porosity distribution and porosity coefficient on nonlinear dynamic response of sandwich beam are presented. The results of this paper could be used to analysis of dynamic modeling for a flexible structure in many industries such as automobiles, Shipbuilding, aircrafts and spacecraft with solar easured at current time step and the velocity and displacement were estimated through linear integration.

• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.83-84
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• 2010

This paper reviews the performance difference between constant voltage control and constant current control in LED driver. Simulations of both control methods are performed for performance comparison especially with temperature variation. The results show that constant current control method is inherently better than constant voltage control for LED drive.

• The Journal of Natural Sciences
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• v.8 no.1
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• pp.17-22
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• 1995

Dielectric constant was measured near the consolute point of a binary mixture of water and Poly[bis(methoxyethoxyethoxy)phosphazene], MEEP. Dielectric constant changed incontinously at phase separation temperature plotted against the concentration to abtain coexistence curve. The critical temperatures and the critical concentration were $71^{\circ}C$, 5.5% as determined from the coexistence curve, respectivley. The critical exponent of dielectric constant, $\theta$, was 0.85. The dependence of dielectric constant on frequency is discussed in this report.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.7
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• pp.1208-1212
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• 2008

In this study, both structural and microwave dielectric properties of the $Ba_5B_4O_{15}$ (B=Ta, Nb) cation-deficient perovskite ceramics with sintering temperature were investigated. All samples of the $Ba_5B_4O_{15}$ (B=Ta, Nb) ceramics were prepared by the conventional mixed oxide method and sintered at $1325^{\circ}C{\sim}1575^{\circ}C$. The bulk density and dielectric constant of the $Ba_5Ta_4O_{15}$ ceramics were increased continuously with increasing of sintering temperature. The quality factor of the $Ba_5Ta_4O_{15}$ ceramics was increased in as the sintering temperature increases from $1375^{\circ}C{\sim}1475^{\circ}C$ but decreased at the temperatures above $1475^{\circ}C$. And the bulk density, dielectric constant and quality factor of the $Ba_5Nb_4O_{15}$ ceramics were increased in as the sintering temperature increases from $1325^{\circ}CP{\sim}1400^{\circ}C$ but decreased at the temperatures above $1400^{\circ}C$. In the case of the $Ba_5Ta_4O_{15}$ sintered at $1475^{\circ}C$ and $Ba_5Nb_4O_{15}$ ceramics sintered at $1400^{\circ}C$, the dielectric constant, quality factor, and temperature coefficient of the resonant frequency (TCRF) were 25.15, 53,105 GHz, -3.06 $ppm/^{\circ}C$ and 39.55, 28,052 GHz, +5.7 ppm/$^{\circ}C$, respectively.

• Ocean Science Journal
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• v.40 no.2
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• pp.79-89
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• 2005

Laboratory radiotracer experiments were conducted to determine assimilation efficiencies (AE) from ingested algal food and oxic sediment particles, uptake rates from the dissolved phase, and the efflux rates of Cd, Cr and Zn in the Asiatic clam Corbicula fluminea. Among three elements, AE from both algal and sediment food was greatest for Cd, followed by Zn and Cr. The AEs of tested elements from algal food (Phaeodactylum tricornutum) were consistently higher than those from sediments at a given salinity and temperature. The influence of salinity (0, 4 and 8 psu) and temperature (5, 13 and $21^{\circ}C$) on the metal AEs was not evident for most tested elements, except Cd AEs from sediment. The rate constant of metal uptake from the dissolved phase $(k_u)$ was greatest for Cd, followed by Zn and Cr in freshwater media. However, in saline water, the $(k_u)$ of Zn were greater than those of Cd. The influx rate of all tested metals increased with temperature. The efflux rate constant was greatest for Cr $(0.02\;d^{-1})$, followed by Zn $(0.010{\sim}0.017\;d^{-1})$ and $Cd\;(0.006\;d^{-1})$. The efflux rate constant for Zn in clam tissues depurated in 0 psu $(0.017\;d^{-1})$ was faster than that in 8 psu $(0.010\;d^{-1})$. Overall results showed that the variation of salinity and temperature in estuarine systems can considerably influence the metal bioaccumulation potential in the estuarine clam C. fluminea. The relatively high Cd accumulation capacity of C. fluminea characterized by the high AE, high dissolved influx rate and low efflux rate, suggested that this clam species can be used as an efficient biomonitor for the Cd contamination in freshwater and estuarine environments.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1420-1421
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• 2006

In this study, structural and micowave dielectric properties of the $Mg_{5}B_{4}O_{15}$ (B=Ta, Nb) cation-deficient perovskite ceeramics. The specimens are prepared through the solid-state route. According to the XRD pattern, $Mg_{4}Ta_{2}O_9$ and $MgTa_{2}O_6$ phase exist in calcined and sintered $Mg_{5}Ta_{4}O_{15}$ powder. Also $Mg_{5}Ta_{4}O_{15}$ phase added with increasing sintering temperature. In the case of calcined and sintered $Mg_{5}Nb_{4}O_{15}$ powder, single phase of $Mg_{5}Nb_{4}O_{15}$ were appeared. The bulk density and quality factor of the $Mg_{5}B_{4}O_{15}$ (B=Ta, Nb) ceramics were increased with sinteming temperature in $1400^{\circ}C{\sim}1450^{\circ}C$, but these were decreased in another sintering temperature. Dielectric constant of the $Mg_{5}Ta_{4}O_{15}$ ceramics was increased continuously with increasing of sintering temperature. And the dielectric constant of the $Mg_{5}Nb_{4}O_{15}$ ceramics was increased in $1400^{\circ}C{\sim}1450^{\circ}C$ but decreased in $1475^{\circ}C$. In the case of the $Mg_{5}Ta_{4}O_{15}$ and $Mg_{5}Nb_{4}O_{15}$ ceramics sintered at $1450^{\circ}C$ for 5h, the dielectric constant, quality factor, and temperature coefficient of the resonant frequency (TCRF) were 8.2, 259,473 GHz, -10.91 $ppm/^{\circ}C$ and 14, 37,350 GHz, -52.3 $ppm/^{\circ}C$, respectively.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.1068-1071
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• 2002

In this study, first, we show that the furnace process which requires maintaining high temperature is effected grievously by the temperature of surrounding air. Second, an alternative which maintains the relatively constant temperature dispersion surrounding the furnace and at the same time has economical advantages will be proposed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.10
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• pp.1172-1177
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• 2004

The emission control of automobile has been intensified as a part of the countermeasure to decrease air pollution in the world. As the cars with an alternative fuel starts to get into the spotlight, the cars with low emission has been introduced and exhaust gas regulation forced in this country. These days, LPG vehicles, which infrastructure of fuel was already built up, and CNG vehicles are recognized for alternative fuel cars in this country. In this study, the constant volume combustion chamber was manufactured and used for experiments to obtain the combustion characteristics of propane mixture. The combustion characteristics was analyzed, with the change of supply conditions of propane fuel. Inside the combustion chamber, the maximum temperature increase with the initial pressure is going up. The burning velocity also seems to have the same characteristic as the temperature. However, the heat flux do not change much according to the theoretical correct mixture but it changes with the various initial temperature of the combustion chamber.

• Transactions on Electrical and Electronic Materials
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• v.10 no.4
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• pp.121-124
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• 2009

In this study, in order to develop compositions of ceramics suitable for piezoelectric actuator and ultrasonic vibrator applications using low temperature sintering, multilayer, PMN-PNN-PZT ceramics were fabricated using $Li_2CO_3$ and $Na_2CO_3$ as sintering aids. Their structural, piezoelectric and dielectric characteristics were investigated according to the Zr/Ti ratio. As the Zr/Ti ratio increased, the electromechanical coupling factor $k_p$, and piezoelectric constant $d_{33}$ and the mechanical quality factor $Q_m$ all increased with Zr/Ti ratio and then decreased after the ratio exceeded 50/50. At the ratio of Zr/Ti =49/51 and sintering temperature of $900^{\circ}C$; the density, electromechanical coupling factor $k_p$, dielectric constant ${\varepsilon}_r$ piezoelectric $d_{33}$ constant and mechanical quality factor $Q_m$ all showed the optimum values of 7.900 $g/cm^3$, 0.576, 856, 312 pC/N, 1,326, respectively. These property values are very suitable for multilayer ceramics actuator applications.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.3
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• pp.75-82
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• 2004

The allowable exhaust standard has been intensified as a part of the countermeasure to decrease air pollution in the world. As the cars with an alternative fuel starts to get into the spotlight, the cars with low emission has been introduced and exhaust gas regulation forced in this country. These days, LPG vehicles, which infrastructure of fuel was already built up, and CNG vehicles are recognized for alternative fuel cars in this country. In this study, the constant volume combustion chamber was manufactured and used for experiments to obtain the ignition characteristics of LPG fuel and the optimal ignition energy. The experiment measured the combustion characteristics, in regard to the change of combustion variable, and the change of ignition energy. During the combustion of fuel, the maximum temperature inside the combustion chamber is higher when the initial pressure is higher. The burning velocity also seems to have the same characteristic as the temperature. However, the heat flux did not change much with the theoretical correct mixture but the various initial temperature of the combustion chamber. The heat flux got faster and ignition energy bigger as the dwell time of the ignition system expanded. When the dwell time get longer, the ignition energy also increased then fixed. The ignition energy increased as the initial pressure inside the combustion chamber higher. The heat flux got faster as the dwell time expanded.