• Earthquakes and Structures
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• v.26 no.4
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• pp.251-259
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• 2024

In this paper, the thermal post-buckling behavior of graphene platelets reinforced metal foams (GPLRMFs) plate with initial geometric imperfections on nonlinear elastic foundations are studied. First, the governing equation is derived based on the first-order shear deformation theory (FSDT) of plate. To obtain a single equation that only contains deflection, the Galerkin principle is employed to solve the governing equation. Subsequently, a comparative analysis was conducted with existing literature, thereby verifying the correctness and reliability of this paper. Finally, considering three GPLs distribution types (GPL-A, GPL-B, and GPL-C) of plates, the effects of initial geometric imperfections, foam distribution types, foam coefficients, GPLs weight fraction, temperature changes, and elastic foundation stiffness on the thermal post-buckling characteristics of the plates were investigated. The results show that the GPL-A distribution pattern exhibits the best buckling resistance. And with the foam coefficient (GPLs weight fraction, elastic foundation stiffness) increases, the deflection change of the plate under thermal load becomes smaller. On the contrary, when the initial geometric imperfection (temperature change) increases, the thermal buckling deflection increases. According to the current research situation, the results of this article can play an important role in the thermal stability analysis of GPLRMFs plates.

• Bulletin of the Korean Chemical Society
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• v.33 no.4
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• pp.1321-1324
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• 2012

• Bulletin of the Korean Chemical Society
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• v.30 no.3
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• pp.731-734
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• 2009

• Bulletin of the Korean Chemical Society
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• v.29 no.5
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• pp.933-938
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• 2008

2,4-Di-(2'-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and polymerized with terephthaloyl chloride and adipoyl chloride to yield novel Y-type polyesters 4 and 5 containing dioxybenzylidenemalononitrile groups as NLO-chromophores, which constituted parts of the polymer backbone. The resulting polymers 4 and 5 are soluble in common organic solvents such as acetone and N,N-dimethylformamide. Polymers 4 and 5 showed thermal stability up to 300 ${^{\circ}C}$ in thermogravimetric analysis with glass-transition temperatures obtained from differential scanning calorimetry in the range 83-94 ${^{\circ}C}$. The second harmonic generation (SHG) coefficients ($d_{33}$) of poled polymer films at the 1064 nm fundamental wavelength were around $6.48\;{\times}\;10^{-9}$ esu. The dipole alignment exhibited high thermal stability even at 10 ${^{\circ}C}$ higher than $T_g$ and no significant SHG decay was observed below 105 ${^{\circ}C}$ partially due to the main-chain character of polymer structure, which is acceptable for NLO device applications.

• Bulletin of the Korean Chemical Society
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• v.31 no.6
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• pp.1509-1514
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• 2010

Methyl 3,4-di-(2'-hydroxyethoxy)benzylidenecyanoacetate (3) was prepared and condensed with terephthaloyl chloride to yield novel Y-type polyester (4) containing 3,4-dioxybenzylidenecyanoacetate groups as NLO-chromophores, which constituted parts of the polymer main chains. The resulting polymer 4 is soluble in common organic solvents such as acetone and N,N-dimethylformamide. Polymer 4 shows thermal stability up to $280^{\circ}C$ in thermogravimetric analysis with glass-transition temperature obtained from differential scanning calorimetry near $105^{\circ}C$. The second harmonic generation (SHG) coefficient ($d_{33}$) of poled polymer films at the 1064 nm fundamental wavelength is around 2.42 pm/V. The dipole alignment exhibits high thermal stability up to near $T_g$, and there is no SHG decay below $100^{\circ}C$ due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.43-48
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• 2003

In this study the optimization of plate-fin type heat sink for the thermal stability is performed numerically. The optimum design variables are obtained when the temperature rise and the pressure drop are minimized simultaneously. The flow and thermal fields are predicted using the finite volume method and the optimization is carried out by using the sequential quadratic programming (SQP) method which is widely used in the constrained nonlinear optimization problem. The results show that when the temperature rise is less than 34.6 K, the optimal design variables are as follows; $B_{1}$ = 2.468 mm, $B_{2}$ = 1.365 mm, and t = 10.962 mm. The Pareto optimal solutions are also presented for the pressure drop and the temperature rise.

• Journal of Ocean Engineering and Technology
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• v.13 no.2 s.32
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• pp.129-137
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• 1999

The time of the onset of double-diffusive convection in time-dependent, nonlinear concentration fields is investigated theoretically. The initially quiescent horizontal fluid layer with a uniform temperature gradient experiences a sudden concentration change from below, but its stable thermal stratification affects concentration effects in such way to invoke convective motion. The related stability analysis, including Soret effect, is conducted on the basis of the propagation theory. Under the linear stability theory the concentration penetration depth is used as a length scaling factor, and the similarity transform for the linearized perturbation equations. The newlly obtained stability equations are solved numerically. The resulting critical time to mark the onset of regular cells are obtained as a function of the thermal Rayleigh number, the solute Rayleigh number, and the Soret effect coefficient. For a certain value of the Soret effect coefficient, the stable thermal gradient promote double-diffusive convective motion.

• Steel and Composite Structures
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• v.41 no.6
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• pp.787-803
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• 2021

The size-dependent nonlinear thermomechanical vibration analysis of pre- and post-buckled tapered two-directional functionally graded (2D-FG) microbeams is presented in this study. In the context of the modified couple stress theory, the formulations are derived based on the parabolic shear deformation beam theory and von Karman nonlinear strains. Different thermomechanical material properties are assumed to be temperature-dependent and smoothly vary in both length and thickness directions using the power law and the physical neutral axis concept is employed. The nonlinear governing equations are derived using the Hamilton principle and the resulting variable coefficient equations of motion are solved using the differential quadrature method (DQM) and iterative Newton's method for clamped-clamped and simply supported boundary conditions. Comparison studies are presented to validate the derived model and solution procedure. The impacts of induced thermal moments, temperature power index, two gradient indices, nonuniform cross-section, and microstructure length scale parameter on the frequency-temperature configurations are explored for both clamped and simply supported microbeams.

• Wind and Structures
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• v.32 no.1
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• pp.31-46
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• 2021

The current research deals with, stability/instability and cylindrical composite nano-scaled shell's resonance frequency filled by graphene nanoplatelets (GPLs) under various thermal conditions (linear and nonlinear thermal loadings). The piece-wise GPL-reinforced composites' material properties change through the orientation of cylindrical nano-sized shell's thickness as the temperature changes. Moreover, in order to model all layers' efficient material properties, nanomechanical model of Halpin-Tsai has been applied. A functionally modified couple stress model (FMCS) has been employed to simulate GPLRC nano-sized shell's size dependency. It is firstly investigated that reaching the relative frequency's percentage to 30% would lead to thermal buckling. The current study's originality is in considering the multifarious influences of GPLRC and thermal loading along with FMCS on GPLRC nano-scaled shell's resonance frequencies, relative frequency, dynamic deflection, and thermal buckling. Furthermore, Hamilton's principle is applied to achieve boundary conditions (BCs) and governing motion equations, while the mentioned equations are solved using an analytical approach. The outcomes reveal that a range of distributions in temperature and other mechanical and configurational characteristics have an essential contribution in GPLRC cylindrical nano-scaled shell's relative frequency change, resonance frequency, stability/instability, and dynamic deflection. The current study's outcomes are practical assumptions for materials science designing, nano-mechanical, and micromechanical systems such as micro-sized sensors and actuators.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.5
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• pp.362-369
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• 2001

The electrical properties of varistors consisting of Zn-Pr-Co-Cr-Er oxides were investigated in the Er$_2$O$_3$content range of 0.0 to 2.0 mol%. the varistors without Er$_2$O$_3$ exhibited a relatively low nonlinearity, which was 14.24 in the nonlinear exponent and 21.47 $\mu$A in the leakage current. However, the varistors with Er$_2$O$_3$ sintered at 1335$^{\circ}C$ for 1h exhibited very high nonlinear exponent of 70, in particular, reaching a maximum value of 78.05 in 2.0 mol% Er$_2$O$_3$, and those sintered at 1335$^{\circ}C$ for 2h exhibited the nonlinear exponent close to 50, in particular, reaching a maximum value of52.76 in 0.5 mol% Er$_2$O$_3$. The others except for 0.5 mol% Er$_2$O$_3$-added varistors exhibited very high instability resulting in a thermal runaway within a short time, even a weak DC stress. Increasing soaking time decreased the nonlinearity, but increased the stability. The varistors containing 0.5mol% Er$_2$O$_3$ sintered for 2h exhibited excellent stability, in which the variation rate of the varistor voltage and nonlinear exponent was -1.70% and -7.15%, respectively, under more severe DC stress such as (0.80 V$_{1mA}$/9$0^{\circ}C$/12h)+(0.85 V$_{1mA}$/115$^{\circ}C$/12h)+(0.90 V$_{1mA}$/12$0^{\circ}C$/12h)+(0.95 V$_{1mA}$/1$25^{\circ}C$/12h)+(0.95 V$_{1mA}$/15$0^{\circ}C$/12h).TEX>/12h).