• East Asian mathematical journal
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• v.32 no.1
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• pp.117-128
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• 2016

In this paper, we study the viscoelastic Kirchhoff type equation with a nonlinear source $$u^{{\prime}{\prime}}-M(x,t,{\parallel}{\bigtriangledown}u(t){\parallel}^2){\bigtriangleup}u+{\int}_0^th(t-{\tau})div[a(x){\bigtriangledown}u({\tau})]d{\tau}+{\mid}u{\mid}^{\gamma}u=0$$. Under the smallness condition with respect to Kirchhoff coefficient and the relaxation function and other assumptions, we prove the uniform decay rate of the Kirchhoff type energy.

• Journal of Magnetics
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• v.4 no.4
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• pp.111-114
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• 1999

Numerical calculation for temperature dependence of galvanomagnetic properties of thin bismuth films is pursued. The quasi-two dimensional system is treated in the perturbation formalism of previous study, where realistic screened potential due to impurity is assumed to be the only scattering channel. The potential is separated into pure two dimensional part and the remaining presumed perturbation part. Relaxation time and mobilities for both electron and hole are evaluated, then temperature dependence of the Hall coefficient and magnetoresistance is obtained. The broad minimum of magnetoresistnace is manifested, and the interpretation under the kinetic theory is made. Thickness dependence of the quantities are also shown, which are in good agreement with the expected quantum size effect.

• Bulletin of the Korean Chemical Society
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• v.14 no.1
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• pp.95-100
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• 1993

A noise-induced transition is presented for a bistable system subjected to a multiplicative random force, which is singular at the unstable state. The stationary probability distribution is obtained from the Fokker-Planck equation and the effects of the singularity is analyzed. On the basis of noise-induced phase transition with Gaussian white noise, the relaxation time and the transition rate of the system are evaluated up to the first order correction of D. In the parameter region v < l, the transition rates decrease as the exponent v goes to 1 and as the coefficient of the linear term of the kinetic equation increases.

• Advances in materials Research
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• v.2 no.1
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• pp.1-13
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• 2013

Lead-free compound $(Na_{0.5}Bi_{0.5})(Zr_{0.75}Ti_{0.25})O_3$ was prepared using conventional ceramic technique at $1070^{\circ}C$/4h in air atmosphere. X-ray diffraction analysis showed the formation of single-phase orthorhombic structure. Permittivity data showed low temperature coefficient of capacitance ($T_{CC}{\approx}5%$) up to $100^{\circ}C$. Complex impedance studies indicated the presence of grain boundary effect, non-Debye type dielectric relaxation and evidences of a negative temperature coefficient of resistance. The ac conductivity data were used to evaluate the density of states at Fermi level and apparent activation energy of the compound.

• Polymer(Korea)
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• v.37 no.6
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• pp.711-716
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• 2013

The effect of chain orientation and relaxation on the characteristics of poly(ethylene naphthalate) (PEN) flexible substrate has been studied. It was found that the coefficient of thermal expansion (CTE) of PEN under $100^{\circ}C$ decreased as low as $20ppm/^{\circ}C$ due to the lowering of chain mobility by chain orientation. The thermal shrinkage was found to appear near glass transition temperature because of chain relaxation. It could be minimized by thermal annealing but CTE increased again up to $70ppm/^{\circ}C$ which was 65% of intrinsic CTE of PEN. Unstrained thermal annealing made possible to avoid the thermal shrinkage with maintaining low CTE obtained by chain orientation. Chain orientation did not affect the optical transmittance; however, thermal annealing caused the decrease of optical transmittance up to 5%. This was understood by the minor crystallization due to the thermal annealing near glass transition temperature.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.53.1-53.1
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• 2011

We analyze the halo and galaxy catalogs from the Millennium simulations at redshifts z=0, 0.5, 1 to determine the alignment profiles of cluster galaxies in terms of the matter density correlation coefficient and discuss a cosmological implication our result has for breaking parameter degeneracies. For each selected cluster, we measure the alignment between the major axes of the pseudo inertia tensors from all satellites within cluster's virial radius and from only those satellites within some smaller radius. Then we average the measured values over the similar-mass sample to determine the cluster galaxy alignment profile as a function of top-hat scale difference at each redshift. It is shown that the alignment profile of cluster galaxies is well approximated by a power-law of the nonlinear density correlation coefficient that is independent of the power spectrum normalization and bias factor. The alignment profile of cluster galaxies is found to have higher amplitude and lower power-law index when averaged over the larger-mass sample and to have rather weak redshift-dependence. This result is consistent with the picture that the satellite galaxies retain the memory of the external tidal fields right after merging and infalling into the clusters but they gradually lose the initial alignment tendency as the cluster's relaxation proceeds. Demonstrating that the nonlinear density correlation coefficient varies sensitively with the density parameter and neutrino mass fraction, we discuss a potential power of the cluster galaxy alignment profile as an independent probe of cosmology.

• Interaction and multiscale mechanics
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• v.4 no.4
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• pp.291-311
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• 2011

To simulate the self excited torsional vibrations of rotating drill strings (DSs) in vertical bore-holes, the nonlinear wave models of homogeneous and sectional torsional pendulums are formulated. The stated problem is shown to be of singularly perturbed type because the coefficient appearing before the second derivative of the constitutive nonlinear differential equation is small. The diapasons ${\omega}_b\leq{\omega}\leq{\omega}_l$ of angular velocity ${\omega}$ of the DS rotation are found, where the torsional auto-oscillations (of limit cycles) of the DS bit are generated. The variation of the limit cycle states, i.e. birth (${\omega}={\omega}_b$), evolution (${\omega}_b&lt;{\omega}&lt;{\omega}_l$) and loss (${\omega}={\omega}_l$), with the increase in angular velocity ${\omega}$ is analyzed. It is observed that firstly, at birth state of bifurcation of the limit cycle, the auto-oscillation generated proceeds in the regime of fast and slow motions (multiscale motion) with very small amplitude and it has a relaxation mode with nearly discontinuous angular velocities of elastic twisting. The vibration amplitude increases as ${\omega}$ increases, and then it decreases as ${\omega}$ approaches ${\omega}_l$. Sectional drill strings are also considered, and the conditions of the solution at the point of the upper and lower section joints are deduced. Besides, the peculiarities of the auto-oscillations of the sectional DSs are discussed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.05a
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• pp.20-23
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• 2001

Hypereutectic Al-25Si alloy, which is expected to be applied to the cylinder-liner-part of the engine-block of an automobile due to its excellent wear resistance, low density and low thermal expansion coefficient, has been fabricated through a spray forming process. The obtained microstructure of the hypereutectic Al-25Si alloy appeared to consist of Al matrix and equiaxed Si particles of average diameter of 5-7 mm. To characterize the deformation behavior of this alloy, a series of load relaxation and compression tests have been conducted at temperatures ranging from RT to $500^{\circ}C$. The strain rate sensitivity parameter (m) of this alloy has been found to be very low (0.1) below $400^{\circ}C$ and reached maximum value of about 0.2 at $500^{\circ}C$. During the deformation above $300^{\circ}C$ in compression, strain softening has been observed. The diagram of extrusion pressure vs. ram-speed has been constructed. The extrusion has been successfully conducted at the temperatures of $300^{\circ}C$ and above with the ratio of area reduction of 28 and 40 in this study.

• Journal of Ginseng Research
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• v.22 no.2
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• pp.96-101
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• 1998

This paper describes the determination of bulk density and the discrimination of internal structure of red ginseng by nuclear magnetic resonance (NMR). The 102 red ginseng roots were tested for bulk density. The NMR properties measured by NMR parameters such as spin-lattice relaxation time ($T_1$) and spin-spin relaxation time ($T_2$) were determined using the low field proton NMR analyzer. Bulk density of red ginseng root showed a highly negative significant correlation (r=-0.8934) with the value of $T_1$, but a highly positive significant correlation (r=0.7672 and 0.5909) with the value of T21 (short T2) and T22 (long T2), respectively. Multiple regression equation, Y=-0.0069.$T_1$+0.3044.$T_{21}$-0.0156.$T_{22}$-0.6368, using the MNR parameter values of 80 red ginseng roots can effectively predict the bulk density of 22 red ginseng roots with the correlation coefficient of 0.9396 and the standard error of 0.086. The differences in the internal structure of normal and inside white part of red ginseng were easily found by the signal intensity of NMR image based on magnetic properties of proton nucleus.

• Mass Spectrometry Letters
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• v.15 no.1
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• pp.54-61
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• 2024

An improved voltage modulation method (VMM) was used to control the heat release and adsorption properties of the adsorbent. In this work, the voltage and flux modulation methods were considered under unified experimental conditions of dissociative surface ionization (SI) of polyatomic organic molecules, the criteria were found when under VMM conditions the current relaxation of SI carries information about the kinetic properties of thermal desorption of ionizable dissociation particles arriving on the surface of polyatomic molecules. Conditions were found under which the relaxation of the ionic current in the flux modulation method is determined by the kinetics of the heterogeneous dissociation reaction of the original polyatomic molecules. The values of the thermal desorption rate constant K⁺ and the activation energy E⁺ obtained with VMM for desorption of (CH₃)₂NCH⁺₂ ions with m/z 58 by adsorption of imipramine and amitriptyline molecules agree well with each other and with the results for the desorption of the same ions by adsorption of other molecules. This confirms one of the basic conditions for the equilibrium process SI - the a degree (β coefficient) of the same particles SI on the same emitter surface is the same and does not depend on the way these particles are formed on the emitter surface.