• Journal of the Korean Ceramic Society
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• v.40 no.11
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• pp.1067-1072
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• 2003

The electrical stability of the varistor ceramics composed of Zn-Pr-Co-Cr-Dy oxides-based varistors was investigated at 0.0∼2.0 mol% Dy$_2$O$_3$ content under DC accelerated aging stress. The ceramic density was increased up to 0.5 mol% Dy$_2$O$_3$ whereas further addition of Dy$_2$O$_3$ decreased sintered ceramic density. The density sailently affected the stability due to the variation of conduction path. The nonlinearity of varistor ceramics was greatly improved above 45 in the nonlinear exponent and below nearly 1.0 ${\mu}$A by incorporating Dy$_2$O$_3$. Under 0.95 V$\_$1mA/150$^{\circ}C$/24 h stress state, the varistor ceramics doped with 0.5 mol% Dy$_2$O$_3$ exhibited the highest electrical stability, in which the variation rates of varistor voltage, nonlinear exponent, and leakage current were -0.9%, -14.4%, and +483.3%, respectively. The variation rates of relative permittivity and dissipation factor were +7.1% and +315.4%, respectively. The varistors with further addition of Dy$_2$O$_3$ exhibited very unstable state resulting in the thermal runaway due to low density.

• 한국가스학회:학술대회논문집
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• 2001.10a
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• pp.35-44
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• 2001

Analytical and experimental studies have been performed to investigate the strength of the membrane and the reaction force at the anchor point. Using nonlinear FEM code and experiments, the stress analysis of the corrugated membrane related the cryogenic liquid pressure and thermal loading is performed to ensure the stability and fatigue strength of the membrane. This paper reports on the FEM results of membrane.

• Journal of Electrical Engineering and information Science
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• v.2 no.6
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• pp.111-115
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• 1997

ZnO varistors are widely used as surge arresters in power system based on their excellent nonlinearity. The property of power loss of ZnO varistors is related to the thermal stability and their life-spans of ZnO surge arresters. The power losses of ZnO varistors under different temperatures and applied voltages were measured, and the properties of power losses were analyzed. The Artificial Neural Network (ANN) was used to simulate the power losses properties of ZnO varistors which is an adaptive nonlinear dynamic system, and the results calculated by ANN simulating model were in good agreement with the tested ones.

• Bulletin of the Korean Chemical Society
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• v.20 no.5
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• pp.567-572
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• 1999

5-Nitro-2-(2'-vinyloxyethoxy)benzylidenemalononitrile (2a), methyl 5-nitro-2-(2'-vinyloxyethoxy)benzylidenecyanoacetate (2b), 3-nitro-4-(2'-vinyloxyethoxy)benzylidenemalononitrile (4a), methyl 3-nitro-4-(2'-vinyloxyethoxy)benzylidenecyanoacetate (4b), 2-nitro-5-(2'-vinyloxyethoxy)benzylidenemalononitrile (6a), and methyl 2-nitro-5-(2'-vinyloxyetboxy)benzylidenecyanoacetate (6b) were prepared by the condensation of 5-nitro-2-(2'-vinyloxyethoxy)benzaldehyde (1), 3-nitro-4-(2'-vinyloxyethoxy)benzaldehyde (3), and 2-nitro-5-(2'-vinyloxyethoxy)benzaldehyde (5) with malononitrile or methyl cyanoacetate, respectively. Vinyl ether monomers 2a-b, 4a-b, and 6a-b were polymerized with boron trifluoride etherate as a cationic initiator to yield poly(vinyl ethers) 7-9 having oxynitrobenzylidenemalononitrile and oxynitrobenzylidenecyanoacetate, which is effective chromophore for second-order nonlinear optical applications. Polymers 7-9 were soluble in common organic solvents such as acetone and DMSO. Tg values of the resulting polymers were in the range of 67-83 ℃. Electrooptic coefficient (r33) of the poled polymer films were in the range of 15-27 pm/V at 633 nm. Polymers 7-9 showed a thermal stability up to 300 ℃ in TGA thermograms, which is acceptable for NLO device applications.

• Bulletin of the Korean Chemical Society
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• v.20 no.3
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• pp.307-313
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• 1999

2,4-Di-(2'-vinyloxyethoxy)benzylidenemalononitrile (la), methyl 2,4-di-(2'-vinyloxyethoxy)benzylidenecyanoacetate (lb), 3,4-di-(2'-vinyloxyethoxy)benzylidene malononitrile (2a), methyl 3,4-di-(2'-vinyloxyethoxy)benzylidenecyanoacetate (2b), 2,5-di-(2'-vinyloxyethoxy)benzylidenemalononitrile (3a), methyl 2,5-di-(2'-vinyloxyethoxy)benzylidenecyanoacetate (3b), 2,3-di-(2'-vinyloxyethoxy)benzylidenemalononitrile (4a), and methyl 2,3-di-(2'-vinyloxyethoxy)benzylidenecyanoacetate (4b) were prepared by the condensation of 2,4-di-(2'-vinyloxyethoxy)benzaldehyde, 3,4-di-(2'-vinyloxyethoxy)benzaldehyde, 2,5-di-(2'-vinyloxyethoxy) benzaldehyde, and 2,3-di-(2'-vinyloxyethoxy)benzaldehyde with malononitrile or methyl cyanoacetate, respectively. Trifunctional divinyl ether monomers 1-4 were polymerized readily with boron trifluoride etherate as a cationic initiator to give optically transparent swelling poly(vinyl ethers) 5-8 havina oxybenzylidenemalononitrile and oxycyanocinnamate, which is presumably effective chromophore for second-order nonlinear optical applications. Polymers 5-8 were not soluble in common organic solvents such as acetone and DMSO due to crosslinking. Polymers 5-8 showed a thermal stability up to 300 ℃ in TGA thermograms, which is acceptable for electrooptic device applications.

• Applied Chemistry for Engineering
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• v.4 no.3
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• pp.482-487
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• 1993

Organic nonlinear optical materials such as MNA(2-Methyl-4-nitro-aniline), Carbazole 1(5-Nitro-9-hydroxyethyl Carbazole), Carbazole 2(5-Nitro-9-ethyl Carbazole) and DR 1(Disperse Red 1) were incorporated into silica matrix to form a composite thin films. The thermal stability and degree of degradation were compared to these organic-inorganic composite film. Among those films, Carbazole 1 and DR 1 which have terminal -OH group showed enhanced stability for thermal degradation. The effect of polarization and degree of relaxation for the composite thin films incorporated with Carbazole 1 were measured by the absorbance change of UV spectra with time. With polarization treatment of Carbazole 1 incorporated composite film, the intensity of UV absorbance was remarkably reduced. And slow relaxation of Carbazole 1 molecule was suggested from the slightly recovered intensity of UV absorbance after removing the electric field at rooma temperature.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.6
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• pp.1385-1394
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• 1994

A three-dimensional numerical model of surface buoyant jets with variable density was established. The model uses fully nonlinear, time-dependent, three-dimensional, ${\sigma}$-transformed equations of motion and equation of heat transport. A semi-implicit numerical scheme in time has been adopted for computational efficiency. The model was applied for thermal jets discharging into a stagnant water and the simulated results were compared with a hydraulic experimental data set showing good agreement. Comparative studies of exchange coefficients and stability functions indicated that spatial variation of exchange coefficients should be considered and the existing stability functions should be modified to simulate surface buoyant jets accurately.

• Structural Engineering and Mechanics
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• v.86 no.4
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• pp.443-459
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• 2023

This study investigates the theoretical thermal buckling analyses of thick porous rectangular functionally graded (FG) plates with different geometrical boundary conditions resting on a Winkler-Pasternak elastic foundation using a new higher-order shear deformation theory (HSDT). This new theory has only four unknowns and involves indeterminate integral variables in which no shear correction factor is required. The variation of material properties across the plate's thickness is considered continuous and varied following a simple power law as a function of volume fractions of the constituents. The effect of porosity with two different types of distribution is also included. The current formulation considers the Von Karman nonlinearity, and the stability equations are developed using the virtual works principle. The thermal gradients are involved and assumed to change across the FG plate's thickness according to nonlinear, linear, and uniform distributions. The accuracy of the newly proposed theory has been validated by comparing the present results with the results obtained from the previously published theories. The effects of porosity, boundary conditions, foundation parameters, power index, plate aspect ratio, and side-to-thickness ratio on the critical buckling temperature are studied and discussed in detail.

• Applied Chemistry for Engineering
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• v.18 no.1
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• pp.77-83
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• 2007

It is essential that second order nonlinear optical materials have low optical propagation losses in the wavelengths of second harmonic generation for practical applications in waveguides. Three dipolar chromophores substituted with nitro, cyano, and alkyl sulfone as an electron withdrawing group were prepared. The UV-Vis absorption spectra of the cyano and alkylsulfone chromophores showed a blue-shift compared to the nitro chromophore. The introduction of oxadiazole segment in the chromophore structure led to similar spectral shift. The blue-shift can produce low optical loses at second harmonics. The chromophores were successfully attached to a polyimide, yielding side chain polymers. The nonlinear optical property of the prepared optical polymers was determined by measuring electro-optic coefficient at 1.55 mm. The polymers exhibited high glass transition temperature of over $185^{\circ}C$ and thermal stability to $300^{\circ}C$ through differential scanning calorimeter analysis and thermal gravimetric analysis.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.6
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• pp.493-500
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• 2014

Nonlinear characteristics of cellular counterflow diffusion flame near the radiative extinction limit at large Damk$\ddot{o}$hler number are numerically investigated. Lewis number is assumed to be 0.5 and flame evolution is calculated by imposing an infinitesimal disturbance to a one-dimensional(1-D) steady state flame. The early stage of nonlinear development is very similar to that predicted in a linear stability analysis. The disturbance with the wavenumber of the fastest growing mode emerges and grows gradually. Eventual, an alternating pattern of reacting and quenching stripes is developed. The cellular flame temperature is higher than that of 1-D flame because of the gain of the total enthalpy. As the Damk$\ddot{o}$hler number is further increased, the shape of the cell becomes circular to increase the surface area per unit reacting volume. The cellular flames do not extinguish but survive even above the 1-D steady state extinction condition.