• Structural Engineering and Mechanics
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• v.57 no.5
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• pp.837-859
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• 2016

An efficient shear deformation theory is developed for wave propagation analysis of an infinite functionally graded plate in the presence of thermal environments. By dividing the transverse displacement into bending and shear parts, the number of unknowns and governing equations of the present theory is reduced, and hence, makes it simple to use. The thermal effects and temperature-dependent material properties are both taken into account. The temperature field is assumed to be a uniform distribution over the plate surface and varied in the thickness direction only. Material properties are assumed to be temperature-dependent, and graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. The governing equations of the wave propagation in the functionally graded plate are derived by employing the Hamilton's principle and the physical neutral surface concept. There is no stretching.bending coupling effect in the neutral surface-based formulation, and consequently, the governing equations and boundary conditions of functionally graded plates based on neutral surface have the simple forms as those of isotropic plates. The analytic dispersion relation of the functionally graded plate is obtained by solving an eigenvalue problem. The effects of the volume fraction distributions and temperature on wave propagation of functionally graded plate are discussed in detail. It can be concluded that the present theory is not only accurate but also simple in predicting the wave propagation characteristics in the functionally graded plate. The results carried out can be used in the ultrasonic inspection techniques and structural health monitoring.

• Journal of the Korean Physical Society
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• v.73 no.11
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• pp.1760-1763
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• 2018

To attain power generation with body heat, the thermal resistance matched design of the thermoelectric generator was the principal factor which was not critical in the case of thermoelectric generator for the waste heat generation. The dimension of thermoelectric legs and the number of thermoelectric leg-pairs dependent output power performances of the thermoelectric generator on the human wrist condition was simulated using 1-dimensional approximated heat flow equations with the temperature dependent material coefficients of the constituent materials and the dimension of the substrate. With the optimum thermoelectric generator design, thermoelectric generator modules were fabricated by using newly developed fabrication processes, which is mass production possible. The electrical properties and the output power characteristics of the fabricated thermoelectric modules were characterized by using a home-made test set-up. The output voltage of the designed thermoelectric generator were a few tens of millivolts and its output power was several hundreds of microwatts under the conditions at the human wrist. The measured output voltage and power of the fabricated thermoelectric generator were slightly lower than those of the designed thermoelectric generator due to several reasons.

• Korean Journal of Materials Research
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• v.29 no.8
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• pp.469-476
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• 2019

A lead-free bulk ceramic having a chemical formula $Ba_{0.8}Ca_{0.2}(Ti_{0.8}Zr_{0.1}Ce_{0.1})O_3$ (further termed as BCTZCO) is synthesized using mixed oxide route. The structural, dielectric, impedance, and conductivity properties, as well as the modulus of the synthesized sample are discussed in the present work. Analysis of X-ray diffraction data obtained at room temperature reveals the existence of some impurity phases. The natural surface morphology shows close packing of grains with few voids. Attempts have been made to study the (a) effect of microstructures containing grains, grain boundaries, and electrodes on impedance and capacitive characteristics, (b) relationship between properties and crystal structure, and (c) nature of the relaxation mechanism of the prepared samples. The relationship between the structure and physical properties is established. The frequency and temperature dependence of the dielectric properties reveal that this complex system has a high dielectric constant and low tangent loss. An analysis of impedance and related parameters illuminates the contributions of grains. The activation energy is determined for only the high temperature region in the temperature dependent AC conductivity graph. Deviation from the Debye behavior is seen in the Nyquist plot at different temperatures. The relaxation mechanism and the electrical transport properties in the sample are investigated with the help of various spectroscopic (i.e., dielectric, modulus, and impedance) techniques. This lead free sample will serve as a base for device engineering.

• Structural Engineering and Mechanics
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• v.70 no.6
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• pp.683-702
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• 2019

The present study aims to analyze the magneto-electro-elastic (MEE) vibration of a functionally graded carbon nanotubes reinforced composites (FG-CNTRC) cylindrical shell. Electro-magnetic loads are applied to the structure and it is located on an elastic foundation which is simulated by visco-Pasternak type. The properties of the nano-composite shell are assumed to be varied by temperature changes. The third-order shear deformation shells theory is used to describe the displacement components and Hamilton's principle is employed to derive the motion differential equations. To obtain the results, Navier's method is used as an analytical solution for simply supported boundary condition and the effect of different parameters such as temperature variations, orientation angle, volume fraction of CNTs, different types of elastic foundation and other prominent parameters on the natural frequencies of the structure are considered and discussed in details. Design more functional structures subjected to multi-physical fields is of applications of this study results.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.11
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• pp.705-709
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• 2017

Effective surface area and morphology of a sensitive thin film are important factors for its applications in sensor systems for the analysis of physical properties. In this study, we investigated the morphologies, electrochemical properties, and applicability of zinc oxide multilayer thin films fabricated by electrodeposition and annealing. The microstructure and electrochemical properties of the zinc oxide films were dependent on temperature and applied voltage. The best characteristics were obtained at an applied voltage of -1.4 V and a temperature of $50^{\circ}C$. The morphologies also changed upon annealing. The results suggest that the zinc oxide films fabricated by electrodeposition and annealing can be applied as various sensor materials.

• Journal of Information Display
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• v.10 no.4
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• pp.175-179
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• 2009

As the physical properties of nematic liquid crystals vary with respect to temperature, the performances of liquid crystal displays (LCDs) are highly dependent on temperature. Additionally, it is well known that the electro-optic characteristics of LCDs, such as transmittance and threshold voltage, also rely on the LCD switching modes. The temperature dependence of the electro-optic characteristics of the wide-viewing-angle LCD modes, such as in-plane switching (IPS), multidomain vertical alignment by patterned electrode (PVA), and fringe-field switching (FFS), have been studied, and the results showed that the FFS mode has lower temperature dependence compared to the IPS and PVA modes. Since the liquid crystal (LC) reorients in different ways in each mode, this result is associated with the temperature dependence of LC's bend and twist elastic constants, and also with the position of the main reorientation, either in the middle or on the surface of the LC layer.

• Geomechanics and Engineering
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• v.19 no.2
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• pp.193-199
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• 2019

A frozen fringe plays a key role in frost heave development in soils. Previous studies have focused on the physical and mechanical properties of the frozen fringe, such as overall hydraulic conductivity, water content and pore pressure. It has been proposed that the thickness of the frozen fringe controls frost heave behavior, but this effect has not been thoroughly evaluated. This study used a temperature-controllable cell to investigate the impact of frozen fringe thickness on the characteristics of frost heave. A series of laboratory tests was performed with various temperature boundary conditions and specimen heights, revealing that: (1) the amount and rate of development of frost heave are dependent on the frozen fringe thickness; (2) the thicker the frozen fringe, the thinner the resulting ice lens; and (3) care must be taken when using the frost heave ratio to characterize frost heave and evaluate frost susceptibility because the frost heave ratio is not a normalized factor but a specimen height-dependent factor.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.13 no.5
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• pp.397-402
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• 2020

Collagen type I is the most abundant protein in the human body. It shows viscoelastic behavior, which is what confers tendons with their viscoelastic properties. There are two different temperature setting methods in molecular dynamics simulations, namely rescaling and reassignment. The rescaling method maintains the temperature by scaling the given temperature, while the reassignment method sets the temperature according to a Maxwell distribution at the target temperature. We observed time-dependent behavior when the reassignment method was applied in tensile simulation, but not when the rescaling method was applied. Time-dependent behavior was observed only when the reassignment method was applied or when one side of the collagen molecule was stretched to a greater extent than the other side. As result, the collagen is elongated to 80nm, 100nm, 130nm, and 180nm, respectively, when the collagen is pulled by different velocities, 0.5, 1, 2, and 5 Å/ps, up to 40 Å. The results do not provide a detailed physical explanation, but the phenomena illustrated in this result are important for caution when further simulations are performed.

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.5-6
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• 2006

Molecular motion at the surface of monodisperse polystyrene (PS) films with various chain end groups was studied by scanning probe microscopy. Surface glass transition temperature ($T_{g^s}$) of the PS films was much lower than the corresponding bulk value. And, the magnitude of $T_{g^s}$ was strongly dependent on chain end chemistry. This result can be explained in terms of the chain end concentration at the surface. Time-temperature superposition principle was applied to rheological analysis at the surface. The apparent activation energy of the surface ${\alpha}_{a}$-relaxation process was approximately a half of that for the bulk sample. This result clearly indicates that the cooperativity for the surface segmental motion was reduced in comparison with that in the bulk region.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2001.02a
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• pp.155-158
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• 2001

An intermediate cooling is indispensible to reduce the refrigeration power at superconducting system that is cooled conductively by a cryocooler without liquid cryogens. The cooling load at the intermediate stage is caused by the mechanical supports, the radiation shield and the current lead. From the cooling load calculation, a thermodynamic analysis that take into account the temperature-dependent properties of the materials and the actual performance of the cryocooler is developed. For any given physical dimensions of the various components, it is shown that there exist a unique optimum for the intermediate temperature to minimize the overall refrigeration power. The results of this study can be usefully applied to the selection of the cryocooler as well as the design of the conduction-cooled cryostat.