• Steel and Composite Structures
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• v.19 no.3
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• pp.713-733
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• 2015

In this paper, viscous fluid induced nonlinear free vibration and instability analysis of a functionally graded carbon nanotube-reinforced composite (CNTRC) cylindrical shell integrated with two uniformly distributed piezoelectric layers on the top and bottom surfaces of the cylindrical shell are presented. Single-walled carbon nanotubes (SWCNTs) are selected as reinforcement and effective material properties of FG-CNTRC cylindrical shell are assumed to be graded through the thickness direction and are estimated through the rule of mixture. The elastic foundation is modeled by temperature-dependent orthotropic Pasternak medium. Considering coupling of mechanical and electrical fields, Mindlin shell theory and Hamilton's principle, the motion equations are derived. Nonlinear frequency and critical fluid velocity of sandwich structure are calculated based on differential quadrature method (DQM). The effects of different parameters such as distribution type of SWCNTs, volume fractions of SWCNTs, elastic medium and temperature gradient are discussed on the vibration and instability behavior of the sandwich structure. Results indicate that considering elastic foundation increases frequency and critical fluid velocity of system.

• Macromolecular Research
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• v.11 no.4
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• pp.250-255
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• 2003

We prepared the photorefractive sol-gel glass based on organic-inorganic hybrid materials containing a charge transporting molecule, second-order nonlinear optical (NLO) chromophore, photosensitizer, and plasticizer. Carbazole and 2-{ 4-[(2-hydroxy-ethyl)-methyl-amino]-benzylidene}-malononitrile were reacted with isocyanato-triethoxy silane and the functionalized silanes were employed to fabricate the efficient photorefractive media induding 2,4,7-trinitrot1uorenone (TNF) to form a charge transfer complex. The prepared sol-gel glass samples showed a large net gain coefficient and high diffraction efficiency at a certain composition. As the concentration of photosensitizer increased, the photorefractive properties were enhanced due to an increment of charge carrier density. Dynamic behavior of the diffraction efficiency was also investigated with the concentration of the photosensitizer.

• Archives of Pharmacal Research
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• v.27 no.5
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• pp.562-569
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• 2004

Self-assembling nanospheres of hydrophobized pullulan have been developed. Pullulan acetate (PA), as hydrophobized pullulan, was synthesized by acetylation. Carboxymethylated poly(ethylene-glycol) (CMPEG) was introduced into pullulan acetate (PA) through a coupling reaction using N, N'-dicyclohexyl carbodiimide (DCC). A synthesized PA-PEG-PA (abbreviated as PEP) conjugate was confirmed by Fourier transform-infrared (FT-IR) spectroscopy. Since PEP conjugates have amphiphilic characteristics in aqueous solution, polymeric nanoparticles of PEP conjugates were prepared using a simple dialysis method in water. From the analysis of fluorescence excitation spectra primarily, the critical association concentration (CAC) of this conjugate was found to be 0.0063 g/L. Observations by scanning electron microscopy (SEM) showed the spherical morphologies of the PEP nanoparticles. The particle size distribution of the PEP conjugates was determined using photon correlation spectroscopy (PCS) and the intensity-average particle size was 193.3 ${\pm}$ 13.53 nm with a unimodal distribution. Clonazepam (CNZ), as a model drug, was easy to entrap into polymeric nanoparticles of the PEP conjugates. The drug release behavior was mainly diffusion controlled from the core portion.

• Journal of Magnetics
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• v.6 no.4
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• pp.132-141
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• 2001

The switching characteristics and the magnetization-flop behavior in magnetic tunnel junctions exchange biased by synthetic antiferromagnets (SyAFs) are investigated by using a computer simulations based on a single-domain multilayer model. The bias field acting on the free layer is found to be sensitive to the thickness of neighboring layers, and the thickness dependence of the bias field is greater at smaller cell dimensions due to larger magnetostatic interactions. The resistance to magnetization flop increases with decreasing cell size due to increased shape anisotropy. When the cell dimensions are small and the synthetic antiferromagnet is weakly, or not pinned, the magnetization directions of the two layers sandwiching the insulating layer are aligned antiparallel due to a strong magnetostatic interaction, resulting in an abnormal magneto resistance (MR) change from the high-MR state to zero, irrespective of the direction of the free-layer switching. The threshold field for magnetization-flop is found to increase linearly with increasing antiferromagnetic exchange coupling in the synthetic antiferromagnet. Irrespective of the magnetic parameters and cell sizes, magnetization flop does not exist near zero applied field, indicating that magnetization flop is driven by the Zeeman energy.

• Archives of Pharmacal Research
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• v.23 no.4
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• pp.367-373
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• 2000

Cholic acid, conjugated with amine-terminated poly(W-isopropylacrylamide) (abbreviated as CA/ATPNIPAAm), was synthesized by a N, N'-dicyclohexyl carbodiimide (DCC)-mediated coupling reaction. Self-assembled CA/ATPNIPAAm micelles were prepared by a diafiltration method in aqueous media. The CA/ATPNIPAAm micelles exhibited a lower critical solution temperature (LCST) at $31.5^{\circ}C$. Micelle sizes measured by photon correlation spectroscopy (PCS) were approximately 31.6 $\times$$\times$ 5.8 nm. The CA/ATPNIPAAm micelles were spherical and their thermal size transition was observed by transmission electron microscope (TEM). A fluorescence probe technique was used for determining the micelle formation behavior of CA/ATPNIPAAm in aqueous solutions using Pyrene as a hydrophobic Probe. The critical micelle concentration (CMC) was evaluated as $8.9{\times}0^{-2}$ g/L. A drug release study was performed using indomethacin (IN) as a hydrophobic model drug. The release kinetics of IN from the CA/ATPNIPAAm micelles revealed a thermo-sensitivity by the unique character of poly(N-isopropylacrylamide) i.e. the release rate was higher at $25^{\circ}C$ than at $37^{\circ}C$.

• Bulletin of the Korean Chemical Society
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• v.24 no.9
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• pp.1276-1280
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• 2003

Thermal behavior of bromphenols was investigated by direct pyrolysis at high temperature. The thermal degradation products formed by the pyrolysis of mono-bromophenols (o-, m-, and p-) were identified by gas chromatography-mass spectrometry. During the pyrolysis reactions, several kinds of dioxins and furans were produced, and the relative ratio of pyro-products was dependent on the substituted position of bromine in phenolic structure due to the effect of symmetry and steric hindrance. The formation of dioxins can be explained by the phenoxy radical addition and Br atom elimination at an ortho-carbon site on phenolic structure. On the other hand, the formation of furans can be explained by the ortho-ortho carbon coupling of phenoxy radicals at unsubstituted sites to form o, o'-dihydroxydiphenyl intermediate via its keto-tautomer, followed by $H_2O$ elimination. The pyrolysis temperature has also a substantial effect on the dimerized products quantities but little effect on the type of pyro-products. Moreover, the formation mechanism of pyro-products was suggested on the basis of products identified.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.4
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• pp.83-90
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• 1987

The applications of reduced integration technique, addition of nonconforming modes, and their coupling to the Mindlin plate elements to improve their basic behavior are reviewed and the establishment of a series of new plate elements by combined use of these schemes are presented in this paper. The element formulation is based upon quadratic Mindlin plate concept. The results obtained by new elements converged to the exact solutions very rapidly as the mesh is refined and showed reliable solutions even for severely distorted meshes. The new elements have the requisite numbers of zero eigenvalues associated with rigid body modes to avoid the spurious zero energy modes. These elements are shown to be applicable to the wide range of plate problems, giving a high accuracy for both thick and thin plates.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.2 s.257
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• pp.182-189
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• 2007

This paper is concerned with the empirical flow stress constitutive equation of steel sheets for an auto-body with the variation of temperature and strain rate. In order to represent the strain rate and temperature dependent behavior of the flow stress at the intermediate strain rates accurately, an empirical hardening equation is suggested by modifying the well-known Khan-Huang-Liang model. The temperature and strain rate dependent sensitivity of the flow stress at the intermediate strain rate is considered in the hardening equation by coupling the strain, the strain rate and the temperature. The hardening equation suggested gives good correlation with experimental results at various intermediate strain rates and temperatures. In order to verify the effectiveness and accuracy of the suggested model quantitatively, the standard deviation of the fitted result from the experimental one is compared with those of the other two well-known empirical constitutive models such as the Johnson-Cook and the Khan-Huang-Liang models. The comparison demonstrates that the suggested model gives relatively well description of experimental results at various strain rates and temperatures.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.8
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• pp.509-514
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• 2010

A numerical simulation of passenger evacuation in a subway station was performed by coupling the passenger flow analysis and the fire simulation. The algorithm of the passenger flow analysis was based on a DEM (Discrete Element Method) using the potential map of the direction vector for each passenger. This algorithm was improved in the present study as to use finer grid smaller than a passenger in order to resolve detailed geometry of the station and to resolve the behavior of passengers in the bottleneck at the ticket gate considering the collision of passengers to a wall or with other passengers. In the fire simulation, the CO distribution predicted by using CFD was used to take into account the effect of toxic gases on the passengers' mobility. The methodology proposed in the present study could be used in designing safer subway station in case of fire occurrence.

• Korean Journal of Crystallography
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• v.7 no.2
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• pp.165-174
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• 1996

The effects of Ba2+, Sr2+, and Ca2+-substitutions for Pb2+ at Pb(Zr0.52Ti0.48)O3 composition were studied for thier dielictric, piezoelectric, and aging properties. For relative dielectric constants and electromechanical coupling factors, the Ba2+-substituted composition was the highest and the Ca2+-substityed composition was the lowest. In the case of mechanical quality factors, the opposite behavior occurred. Time dependence of frequency for various ion-substituted compositions is similar to that of non-substituted composition. The piezoelectric properties after aging at high temperature was the worse than that after aging at room temperature.