• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.12
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• pp.1021-1026
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• 2016

In this study, crack resistance is evaluated by the crack tip opening angle (CTOA) using a wedge splitting test (WST) on a viscoelastic particulate reinforced composite based on an HTPB binder. Generally, CTOA, as a function of crack extension, is used in order to determinate fracture resistance and has a steady state relative angle. Digital image correlation (DIC) is used to measure the crack tip opening displacement (CTOD) and crack extension for the critical crack tip opening angle (CTOAc). In these results, the CTOAc value of a particulate reinforced composite tends to approach a constant angle after a small amount of crack extension. The CTOAc value increases with decreasing temperature, from $50^{\circ}C$ to $-40^{\circ}C$. These CTOAc values may be used to measure fracture mechanics parameters for particulate reinforced composite.

• Applied Chemistry for Engineering
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• v.32 no.1
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• pp.15-19
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• 2021

In this study, we studied a facile method for the synthesis of stable and nearly spherical gold nanoparticles using a tyrosine-rich peptide, Tyr-Tyr-Gly-Tyr-Tyr (YYGYY), as both the reducing and capping agent. The peptide coated spherical and polycrystalline gold nanoparticles with diameters from 3 to 15 nm were successfully synthesized by varying the concentration of the peptide and metal precursor under UV irradiation. The nanoparticles were then characterized by transmission electron microscopy (TEM), UV-Vis spectroscopy, scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). Furthermore, the catalytic activity of gold nanoparticles was confirmed by the reduction of 4-nitrophenol to 4-aminophenol, in which the catalytic reaction rate constant was 7.3 × 10-3 s-1.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.9
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• pp.420-426
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• 2018

Acoustic Quanta, which British Physicist Dennis Gabor created, is the theoretical background for granular synthesis and has influenced many computer music artists and sound designers. Acoustic Quanta is a very short sound burst, lasting only 1 to 100 ms. Granular synthesis is a sound synthesis technique which slices original sound into sound grains and re-combines them into a new acoustic event. Concept of sound grain is borrowed from the acoustic quanta. Granular Synthesis can make very unique sound, so that it can be useful in many ways, especially in sound design. This paper presents concept of acoustic quanta and granular synthesis. It then discusses making a synthesizer as an implementation of synchronous granular synthesis and its applications on sound design. As a result, the duration of acoustic quanta should range between 0.239 and 33.367 ms, in consideration of audible frequencies, which is different from the original concept of the acoustic quanta.

• ICROS
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• v.8 no.6
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• pp.18-22
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• 2002

• Applied Chemistry for Engineering
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• v.27 no.4
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• pp.449-454
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• 2016

In this study, highly monodispersed porous carbon microcapsules with a hollow core were synthesized using polystyrene (PS) beads as a hard template. The surface of PS was first modified with polyvinylpyrollidone (PVP) for the easy attachment of inorganic silica sol. After coating the surface of PVP modified PS microspheres with SBA-16 sol, the carbon microcapsules with a hollow macroporous core were fabricated through reverse replication method by filling carbon sources in the mesopores of silica mold. The hollow carbons having a mesoporous shell structure and narrow particle size distribution could be obtained after the carbonization of carbon source and the dissolution of silica mold by HF solution. The mesoporous characteristics and electrochemical properties of hollow carbon microcapsules were characterized by XRD, SEM, TEM, $N_2$ adsorption/desorption analysis and cyclic voltammetry. They showed the high electric conductivity and capability for use as efficient electro-materials such as a supercapacitor.

• Applied Chemistry for Engineering
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• v.27 no.1
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• pp.68-73
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• 2016

Silver nanoparticles were prepared by chemical reduction-protection method using 1-decanoic acid and tri-n-octylphosphine as surfactants, and using $NaBH_4$ as a reducing agent. The silver nanoparticles were also studied for their formation, structure, morphology and size using UV-Visible spectroscopy, XRD, TEM and SEM. Further the viscosity of the silver paste and the surface resistance of the silver metal film produced by screen coating onto a PET film were investigated. Well dispersed and quasispherical silver nanoparticles with the size of 10-200 nm were obtained under the optimal molar ratio of $NaBH_4/AgNO_3=1:5$. The surface resistance of silver metal film coated on the PET film made with the silver nanoparticles under the optimal molar ratio showed a minal value of $41{\mu}{\Omega}/cm^2$.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.20 no.1
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• pp.64-81
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• 1994

O/W emulsions with mixed nonionic surfactants(polyoxyethylene(20)sorbitan monostearate/sorbitan sesquioleate), liquid paraffin, water prepared by direct inversion emulisification method and continuous inversion emulsification Method. The one-step, two-step and three-step phase inversion emulsification method were used in experiments. Effect of added water on droplet size of final O/W emulsions which is prepared by phase inversion emulsification method were investigated. In direct inversion emulsification method(two-step emulsification method), fine and homogeneous droplets of OIW emulsions were formed after phase inversion steps i.e. ,W/O - (W/O) If double emulsion - O/W emulsion. In continuous inversion emulsification method(three-step emulsification method), fine and homogeneous O/W emulsion were formed after phase inversion steps i.e., W/O - pseudomicroemulsion - O/W. By latter method, more Fine and homogenuous droplets were formed than former method. 10-10, 8 HLB region of mixed non-ionic surfactants could produce most fine droplets. This HLB region had maximum values of solubilization water and This HLB value of mixed nonionic surfactants produced fine and homogenuous droplets.

• Journal of the Korean Magnetics Society
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• v.16 no.1
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• pp.66-70
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• 2006

Magnetite nanoparticles, which have been extensively used in many fields, were encapsulated with a natural polymer, chitosan, to improve their biocompatibility. We have synthesized magnetite $(Fe_3C_4)$ nanoparticles using chemical coprecipitation technique with sodium oleate as surfactant. Nanoparticle size can be varied from 1.2 to 7.4nm by controlling the sodium oleate concentration. Magnetite phase nanoparticles could be observed from X-ray diffraction. Magnetic colloid suspensions containing particles with sodium oleate and chitosan have been prepared. High magnetic property chitosan-microsphere particles were prepared from oleate-coated magnetite suspension using spray method. The surftce, and tile morphology of the magnetic chitosan microsphere particles were characterized using optical microscope and scanning electron microscope. Magnetic hysteresis measurement were performed using a superconducting quantum interference device (SQUID) magnetometer at room temperature to investigate the magnetic properties of the chitosan microspheres including magnetite nanoparticles. The SQUID measurements revealed superparamagnetism of nanoparticles.

• Korean Chemical Engineering Research
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• v.49 no.6
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• pp.752-757
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• 2011

The effects of reaction temperature, reactant concentration, pH of solution and mixing order of reactants on the particle shape and size distribution of zinc oxide were investigated in the preparation of zinc oxide from ammonium hydroxide and zinc acetate by the method of aqueous hydrothermal precipitation method, and the photocatalytic ability of zinc oxide synthesized was measured from the degradation of tartrazine under UV irradiation. The average particle size was increased with pH of solution but decreased with zinc acetate concentration and reaction temperature. The optimum condition for the synthesis of minimum sized zinc oxide was pH 11.2, concentration of zinc acetate 0.6 M and reaction temperature $90^{\circ}C$, and its average particle size was 3.133 ${\mu}$m. 97% of tartrazine was degraded by zinc oxide in sixty minutes.

• Nuclear Engineering and Technology
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• v.21 no.1
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• pp.40-47
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• 1989

For the effective design of a beam forming structure of the negative-ion-based neutral beam injector, a computer program based on a particle simulation model is developed for the calculation of charged particle motions in the electrostatic fields. The motions of negative ions inside the acceleration tube of a multiple-aperture triode are computed at finite time steps. The electrostatic potentials are obtained from the Poisson's equation by the finite difference method. The successive overrelaxation method is used to solve the matrix equation. The particle and force weighting methods are used on a cloud-in-cell model. The optimum design of the beam forming structure has been studied by using this computer code for the various conditions of elctrodes. The effects of the acceleration-deceleration gap distance, the thickness of the deceleration electrode and the shape of the acceleration electrode on beam trajectories are exmined to find the minimum beam divergence. Some numerical illustrations are presented for the particle movements at finite time steps in the beam forming tubes. It is found in this particle simulation modelling that the shape of the acceleration electrode is the most significant factor of beam divergence.