• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.5
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• pp.300-306
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• 2018

The rod-shaped $Ni_{0.5}Zn_{0.5}Fe_2O_4$ particles were synthesized via a topotactic reaction, in which goethite (${\alpha}-FeOOH$) particles are the main constituents. The phases, microstructures and magnetic properties of these particles were studied using XRD, FE-SEM and VSM. The precursor solution consisted of $NiSO_4{\cdot}xH_2O$, $ZnSO_4{\cdot}xH_2O$, goethite and D.I. water werereacted at four different temperatures (50, 70, 90, $100^{\circ}C$) to generate four differently precipitated particles respectively. During the co-precipitation reaction, the pH of the solution was maintained at 8.0 using NaOH. The particles co-precipitated and calcined at a temperature of $700^{\circ}C$, exhibited a rod-shape similar to its original goethite, which means that the shape of Ni-Zn ferrite particles can be topotactically controlled by the goethite. The particles synthesized at 70 and $90^{\circ}C$ have a saturation magnetization of 29 and 35 emu/g respectively; representing better values than the ones synthesized at the 50 and $100^{\circ}C$, in which some second phases such as $Fe_2O_3$ were observed.

• Korean Journal of Optics and Photonics
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• v.24 no.6
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• pp.338-341
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• 2013

Prothrombin Time (PT) is used as a measure of blood coagulation time. An optical analysis of the signal generating mechanism is described here for the reflection-type arrangement. Thromboplastin added into serum or whole blood initiates the coagulation process. We added a sufficient amount of magnetic particles into the sample before adding thromboplastin and subjected the mixture to a rotating magnetic field. The laser light gets reflected in a periodically modulated fashion with respect to the magnetic field rotation. Analysis of this decaying modulation could produce a reasonable coagulation time. We also introduce a simulation model to explain the signal generating mechanism using LightTools.$^{TM}$

• Korean Journal of Materials Research
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• v.22 no.3
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• pp.136-139
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• 2012

Magnetic nanoparticles for ferromagnetic fluids and magnetorheological fluids were prepared by chemical coprecipitation and mechanical milling, respectively. The surface-treated particles were dispersed at various weight ratios into a medium of polyethylene glycol. In order to evaluate the elastic modulus of the fluids, ultrasonic pulse velocities were measured with an ultrasonic test using transducers of 5MHz and 2.25MHz. The ultrasonic signals were only available with a transducer of 2.25 MHz at fluid concentrations of 5 mg/ml and lower. In the case of applying transducers over 2.25 MHz and concentrations over 5 mg/ml to the fluids, it was impossible to observe effective ultrasonic signals due to an excessive scattering of the pulses by the dispersed particles. Elastic moduli of the magnetorheological fluids were 5.44 GPa and 6.13 GPa with concentrations of 25 mg/ml and 50 mg/ml, respectively; these values were higher by 40% than the values of 4.04 GPa and 4.28 GPa of ferromagnetic fluids at the same concentrations. As for the effect of an external magnetic field on these dilute fluids, the ultrasonic signals were positioned in a very similar way, which was probably due to insufficient arrangement of the particles even though the reflection energy of the ultrasonic waves apparently increased.

• Journal of the Korean Magnetics Society
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• v.16 no.4
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• pp.221-227
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• 2006

We have synthesized uniform nanometer sized magnetite particles using chemical coprecipitation technique through a sonochemical method with surfactant such as oleic acid. Magnetite phase nanoparticles could be observed from X-ray diffraction. Magnetite nanoparticles is surface phase morphology and biopolymer-microspheres for Application Medical. Magnetite nanoparticles coated biopolymer. Atomic Force Microscope (AFM) was used to image the coated nanoparticles. Magnetic colloid suspensions containing particles with sodium oleate, chitosan and $\beta$-glucan have been prepared. The morphology of the magnetic biopolymer microsphere particles were characterized using optical microscope. Magnetic hysteresis measurement were performed using a superconducting quantum interference device (SQUID) magnetometer at room temperature to investigate the magnetic properties of the biopolymer microspheres and magnetite coated biopolymer including magnetite nanoparticles. Magnetic Resonance (MR) imaging was used to investigate biopolymer coated nanoparticles and biopolymer microspheres.

• Journal of Powder Materials
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• v.11 no.1
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• pp.16-21
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• 2004

The nano-sized Co particles were successfully synthesized by chemical vapor condensation (CVC) process using the precursor of cobalt carbonyl ($Co_2(CO)_8$). The influence of carrier gases on the microstructure and magnetic properties of nanoparticles was investigated by means of XRD, TEM, XPS and VSM. The Co nano-particles with different phases and shapes were synthesized with a change of carrier gas : long string morphologies with coexistence of fcc and hcp structure in Ar carrier gas condition; finer Co core in a mass of cobalt oxide with only fcc structure in He; rod type cobalt oxide phase in Ar＋6vol％$O_2$. The saturation magnetization and coercivity was lower in Co nanoparticles synthesized in He carrier gas, due to their finer size.

• Journal of the Korean Ceramic Society
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• v.11 no.1
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• pp.23-28
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• 1974

1. Stage crushing by jaw crusher, steel mortar, and ball mill in turn has shown an inclination to increase the distribution of andalusite in coarse particles as well as to increase that of micas in fine particles. 2. Water elutriation was effective for the removal of muscovite and magnetic separation was effective for that of Mg-Fe micas such as biotte and chlorite. The process of concentration and that of purification are diagramatized respectively as follows: Concentration; Raw andalusite${\lightarrow}$Crushing${\lightarrow}$Screening${\lightarrow}$Water elutriation${\lightarrow}$Magnetic separation Purification; Concentrated andalusite${\lightarrow}$Calcination${\lightarrow}$Ball milling${\lightarrow}$Screening${\lightarrow}$Water elutriation${\lightarrow}$Magnetic separation${\lightarrow}$Acid washing.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1241-1242
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• 2006

Electromagnetic properties of $CeO_2$ doped and undoped YBaCuO superconductors were evaluated to investigate the effect of pinning center on the magnetization and magnetic shielding. The variation $\DeltaM$ with doping was maximum for 3% doping and decrease with further doping. The magnetic shielding was evaluated by measuring the induced voltage in secondary coil and the voltage initially set to 0.5V, decreased to 0.17V and 0.28V respectively for the undoped and 3% $CeO_2$ doped sample. The much less change in the induced voltage for the 3% doped sample is attributed to the increased flux shielding by shielding vortex current. The $CeO_2$ was converted to fine $BaCeO_3$ particles which were trapped in YBaCuO superconductor during the reaction sintering. The trapped fine particles, $BaCeO_3$ may be acted as a flux pinning center.

• Progress in Superconductivity and Cryogenics
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• v.23 no.3
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• pp.26-31
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• 2021

Advanced classification of Cs contaminated soil by using a magnetic force-assisted selection pipe was investigated. A selection pipe is a device that sort particles depending on their particle size, based on the relationship between buoyancy, drag, and gravity force acting on the particles. Radioactive cesium is concentrated in small-particle size soil components with a large specific surface area. Hence, the volume of the Cs contaminated soil can be reduced by recycling the large-particle size soil components with low radioactive concentration. One of the problems of the selection pipe was that the radioactive concentration of the stayed soil in the selection pipe exceeds 8000 Bq/kg, which is the standard value of recycling of Cs contaminated soil, due to low classification accuracy. In this study, magnetic fields were applied to the lab-scale selection pipe from upper side to improve the classification accuracy and to reduce the radioactive concentration of the stayed soil.

• Journal of The Korean Astronomical Society
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• v.37 no.5
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• pp.439-446
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• 2004

A critical discussion of our knowledge about extragalactic cosmic rays and magnetic fields is at-tempted. What do we know for sure? What are our prejudices? How do we confront our models with the observations? How can we assess the uncertainties in our modeling and in our observations? Unfortunately, perfect answers to these questions can not be given. Instead, I describe efforts I am involved in to gain reliable information about relativistic particles and magnetic fields in extragalactic space.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.446-447
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• 2006

Magnetic oxide-coated iron nanoparticles with the mean size ranging from 6 to 75 nm were synthesized by aerosol method using iron carbonyl as a precursor under the flowing inert gas atmosphere. Oxide shells were formed by passivation of asprepared iron particles. The influence of experimental parameters on the nanoparticles' microstructure, phase composition and growth behavior as well as magnetic properties were investigated and discussed in this study.