• Structural Engineering and Mechanics
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• v.91 no.6
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• pp.539-549
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• 2024

In this paper, thermal buckling analysis was conducted using trigonometric shear deformation theory, which employs only four unknowns instead of five. This present theory is variationally consistent, and accounts for a trigonometric variation of the transverse shear strains across the thickness and satisfies the zero traction boundary conditions on the top and bottom surfaces of the plate without using shear correction factors. The grading is provided along the thickness of the plate as per power law volume fraction variation of metal-matrix ceramic reinforced composite. The non-linear governing equation problem was solved for simply supported boundary conditions. Three types of thermal loads are assumed in this work: uniform, linear and non-linear distribution through-the-thickness. It is well known that material properties change with temperature variations and so the analysis was performed for both the cases: temperature-dependent (TD) and temperature-independent (TID) material properties. The impact on thermal buckling for both linear and non-linear temperature variation was considered. The results were validated for the TID case with other theories and were found to be in good agreement. Furthermore, a comprehensive analysis was performed to study the impact of grading indices and geometrical parameters, such as aspect ratio (a/b) and side-to-thickness ratio (a/h), on the thermal buckling of the FG plate.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.2
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• pp.185-191
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• 2008

Optimal damping layout of the constrained viscoelastic damping layer on beam is identified with temperatures by using a gradient-based numerical search algorithm. An optimal design problem is defined in order to determine the constrained damping layer configuration. A finite element formulation is introduced to model the constrained layer damping beam. The four-parameter fractional derivative model and the Arrhenius shift factor are used to describe dynamic characteristics of viscoelastic material with respect to frequency and temperature. Frequency-dependent complex-valued eigenvalue problems are solved by using a simple re-substitution algorithm in order to obtain the loss factor of each mode and responses of the structure. The results of the numerical example show that the proposed method can reduce frequency responses of beam at peaks only by reconfiguring the layout of constrained damping layer within a limited weight constraint.

• Journal of the Korean Chemical Society
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• v.19 no.3
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• pp.149-155
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• 1975

Pivalic acid, which has a globular shape and is a plastic crystal, has been examined by means of temperature-dependent with-line proton magnetic resonance spectroscopy. Results of temperature-dependent line width, second moment, and spin-lattice relaxation time studies of pivalic acid were interpreted in terms of dynamic behavior and hydrogen bonding. The dynamic behavior consists of superimposed reorientation of the methyl groups about their three-fold axes$(C_3) and of the molecule about the central C-C bond(C_3'),$ general molecular reorientation about the center of gravity, and molecular self-diffusion. Activation energies for the motional processes have been obtained from line width measurements using the modified Bloembergen, Purcell, and Pound theory and from spin-lattice relaxation time measurements. The results were compared with the Pople-Karasz theory of fusion and the agreement was found to be poor. The discrepancy was interpreted in terms of hydrogen bonding in this molecule.

• Smart Structures and Systems
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• v.24 no.2
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• pp.267-292
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• 2019

The present article addresses the coupled free vibration problem of skew magneto-electro-elastic plates (SMEE) considering the temperature-moisture dependent material properties. The plate kinematics follows Reddy's higher order shear deformation theory. With the aid of finite element methods, the governing equations of motion are derived considering the Hamilton's principle and solved by adopting condensation technique. The influence of different temperature and moisture dependent empirical constants on the frequency response of SMEE plate has been assessed. In addition, the natural frequencies corresponding to various fields are evaluated and the effect of empirical constants on these coupled frequencies is determined. A detailed parametric study has been carried out to assess the individual effects of temperature and moisture dependent empirical constants along with their combined effect, aspect ratio, length-to-width ratio, stacking sequence and boundary conditions. The results reveal that the external environment as well as the geometrical skewness has a significant influence on the stiffness of the SMEE plates.

• Advances in nano research
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• v.12 no.3
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• pp.231-251
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• 2022

Dynamic behavior of temperature-dependent Reddy functionally graded (RFG) nanobeam subjected to thermomagnetic effects under the action of moving point load is carried out in the present work. Both symmetric and sigmoid functionally graded material distributions throughout the beam thickness are considered. To consider the significance of strain-stress gradient field, a material length scale parameter (LSP) is introduced while the significance of nonlocal elastic stress field is considered by introducing a nonlocal parameter (NP). In the framework of the nonlocal strain gradient theory (NSGT), the dynamic equations of motion are derived through Hamilton's principle. Navier approach is employed to solve the resulting equations of motion of the functionally graded (FG) nanoscale beam. The developed model is verified and compared with the available previous results and good agreement is observed. Effects of through-thickness variation of FG material distribution, beam aspect ratio, temperature variation, and magnetic field as well as the size-dependent parameters on the dynamic behavior are investigated. Introduction of the magnetic effect creates a hardening effect; therefore, higher values of natural frequencies are obtained while smaller values of the transverse deflections are produced. The obtained results can be useful as reference solutions for future dynamic and control analysis of FG nanobeams reinforced nanocomposites under thermomagnetic effects.

• Journal of the Korean Physical Society
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• v.81
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• pp.133-138
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• 2022

Using the first principles calculations, we investigated the strain dependent magnetic properties of the 1T-VSe₂ monolayer (up to ± 3%). We obtained a metallic band structure, and this feature was preserved under both compressive and tensile strain. The pristine system had a magnetic moment of 0.9 µ_B/unit cell and decreased to 0.68 µ_B/unit cell under - 3% compressive strain whereas it was increased to 1.03 µ_B/unit cell under + 3% tensile strain. The 1T-VSe₂ monolayer had an in-plane magnetic anisotropy with a value of - 0.48 meV/cell. The in-plane anisotropy features were maintained in both compressive and tensile strains. The orbital resolved magnetic anisotropy indicated that the V atom contributed to the perpendicular magnetic anisotropy while the Se atom had an in-plane anisotropy. We found that the Se dominated the anisotropy. We also calculated the temperature dependent Curie temperature (T_C). The pristine structure had a T_C of 260 K, and the strain effect enhanced the T_C. Particularly, the compressive strain affected further the exchange parameter resulting in substantial enhancement of the Curie temperature where a T_C of 570 K was achieved at - 3% strain. Our finding regarding the strained VSe₂ could help for further investigation in spintronics and straintronics applications.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1755-1758
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• 2004

Misfiring is often observed during the high temperature quality assurancetest of plasma display panel. This limits the productivity of PDP industry. In this paper, experimental observations on the misfiring at high panel temperature have been performed through time dependent discharge light output and static margin measurement. For the high temperature condition, firing voltage increment is found in both surface and facing discharges. This in turn increases lime lag in address discharge, and results m increment of misfiring probability. In order to reduce this kind of misfiring, a new method that applies automatically different slope of ramp erasing pulse on the common electrode according to temperature variation is proposed. The experimental results show that controlling the slope of ramp erasing pulse is quite effective for compensating temperature-dependent variation of reset and address discharge.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.164-170
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• 2004

Misfiring is often observed during the high temperature quality assurance test of plasma display panel. This limits the productivity of PDP industry. In this paper, experimental observations on the misfiring at high panel temperature have been performed through time dependent discharge light output and static margin measurement. For the high temperature condition, firing voltage increment is found in both surface and facing discharges. This in turn increases time lag in address discharge, and results in increment of misfiring probability. In order to reduce this kind of misfiring, a new method that applies automatically different slope of ramp erasing pulse on the common electrode according to temperature variation is proposed. The experimental results show that controlling the slope of ramp erasing pulse is quite effective for compensating temperature-dependent variation of reset and address discharge.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.403-406
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• 2002

A number of the experiments on the phenomenon in which the thermal energy was transferred from a hot sphere to the surrounding water through the film boiling process had been conducted. As the sphere only carried the thermal energy associated with its initially high temperature but did not contain any other thermal source, the film boiling was only driven by the decreasing temperature of the sphere and, thus, was time dependent. The results from the experiments showed that the temperature of the sphere was slowly decreased in the beginning. This corresponded to the period in which the sphere was penetrating the water surface. Later, when the sphere was fully submerged and the transition film boiling was observed over the whole surface, the temperature of the sphere was decreased relatively much faster. In the last stage, the temperature of the sphere was again slowly decreased. This was considered caused by the relatively low temperature of the sphere, which reduced and later ceased the film boiling process. In addition, the estimation of the departure rate of the steam bubbles from the film layer was also correlated for the experiments.

• Journal of ILASS-Korea
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• v.19 no.4
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• pp.174-181
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• 2014

This study investigates the effects of nanoparticle size and temperature on the thermal conductivity enhancement of water-based alumina ($Al_2O_3$) nanofluids, using the centrifuging method and relative centrifugal forces of differing magnitude to produce nanofluids of three different particles without involving any dispersants or surfactants. We determined the coupling dependency in thermal conductivity enhancement relative to nanoparticle size and temperature of the alumina nanofluids and also experimentally showed that the effect of temperature on thermal conductivity is strongly dependent on nanoparticle size. Also, our experimental data presented that the effective medium theory models such as the Maxwell model and Hasselman and Johnson model are not sufficient to explain the thermal conductivity of nanofluids since they cannot account for the temperature- and size-dependent nature of water-based alumina nanofluids.