• Journal of Magnetics
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• v.8 no.1
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• pp.7-12
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• 2003

The method for evaluation of the particle size distribution of fine particles from hysteresis loop measurements is Presented. The method is illustrated on the SiO$_2$-based Co nanoparticle systems. The influence of technological conditions of sample preparation onto particle size distribution is investigated.

• Journal of The Korean Astronomical Society
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• v.46 no.1
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• pp.49-63
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• 2013

Nonthermal radiation from supernova remnants (SNRs) provides observational evidence and constraints on the diffusive shock acceleration (DSA) hypothesis for the origins of Galactic cosmic rays (CRs). Recently it has been recognized that a variety of plasma wave-particle interactions operate at astrophysical shocks and the detailed outcomes of DSA are governed by their complex and nonlinear interrelationships. Here we calculate the energy spectra of CR protons and electrons accelerated at Type Ia SNRs, using time-dependent, DSA simulations with phenomenological models for magnetic field amplification due to CR streaming instabilities, Alf$\acute{e}$enic drift, and free escape boundary. We show that, if scattering centers drift with the Alf$\acute{e}$en speed in the amplified magnetic fields, the CR energy spectrum is steepened and the acceleration efficiency is significantly reduced at strong CR modified SNR shocks. Even with fast Afv$\acute{e}$nic drift, DSA can still be efficient enough to develop a substantial shock precursor due to CR pressure feedback and convert about 20-30% of the SN explosion energy into CRs. Since the high energy end of the CR proton spectrum is composed of the particles that are injected in the early stages, in order to predict nonthermal emissions, especially in X-ray and ${\gamma}-ray$ bands, it is important to follow the time dependent evolution of the shock dynamics, CR injection process, magnetic field amplification, and particle escape. Thus it is crucial to understand the details of these plasma interactions associated with collisionless shocks in successful modeling of nonlinear DSA.

• Journal of the Korean Magnetics Society
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• v.4 no.3
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• pp.282-284
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• 1994

A theoretical expression for determining the effective magnetic moment of hematite(${\alpha}-Fe_{2}O_{3}$) particle of the parasitic ferromagnetism by the proton relaxation in water is derived. In deriving the expression it is found that the mathematical procedures are exactly the same as those applied for aqueous solutions containing free paramagnetic ions, except that the distance between the proton spin of water molecule and the corresponding electronic spin of the particle must be considered to be a radius vector rather than a relative distance. And it is also found that the average effective magnetic moment of the particle calculated by the expression is in good agreement with the experimental value determined by Hirai.

• Journal of the Korean Chemical Society
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• v.56 no.5
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• pp.609-616
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• 2012

Ba-ferrite ($BaFe_{12}O_{19}$) nanoparticles were synthesized by chemical coprecipitation method in an aqueous solution. The particle size and the crystallization temperature of the Ba-ferrite nanoparticles were controlled varying the precipitation temperature. The precipitate that was prepared at $0^{\circ}C$ showed the crystal structure of Ba-ferrite in X-ray diffraction when it was calcined at the temperature above $580^{\circ}C$, whereas what was prepared at $50^{\circ}C$ showed the crystallinity when it was calcined at the temperature higher than about $700^{\circ}C$. The particle sizes of the synthesized Ba-ferrite were in a range of about 20-30 nm when it was prepared by being precipitated at $0^{\circ}C$ and calcined at $650^{\circ}C$. When the precipitation temperature increased, the particle size also increased even at the same calcination temperature. The magnetic properties of the Ba-ferrite nanoparticles were also controlled by the synthetic condition of precipitation and calcination temperature. The coercive force could be appreciably lowered without a loss of saturation magnetization when the Ba-ferrite nanoparticles were prepared by precipitation and calcination both at low temperatures.

• Journal of the Korean Ceramic Society
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• v.26 no.6
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• pp.737-746
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• 1989

After Ba-ferrite powders synthesized hydrothermally and its heated powders were dissolved partially with HCl treatment time, the BaO/Fe2O3 mole ratio of dissolved solutions and powders were measured by AAS, also, lattice constants, particle morphology and magnetic properties in HCl treated, heated and no-heated Ba-ferrite powders were abtained by means of XRD, SEM and VSM, respectively. From above analysis results, the effect of Ba/Fe mole ration in suspension(as starting material) on the BaO/Fe2O3 composition and particle characteristics of products were investigated, and the effect of heat treatment on magnetic properties of products examined. The composition, lattice constant and crystal phase of products depend on the Ba/Fe mole ratio in suspension. Ba content in surface or outer part of Ba-ferrite powder is higher than inner and heterogeneous, and the excess Ba ions in the inner part of particle move into the outer by heating, so that the mole ratio of BaO/Fe2O3 in the more jinner approaches more to the stoichiometric composition 1 : 6. The crystallinity, coercivity and saturation magnetization of products are increased by heat treatment, and the heat-treated samples synthesized hydrothermally in lower temperature are appreciated to have better powder characteristics.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.545-548
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• 2015

Most high energy cosmic rays (CRs) are thought to be produced by diffusive shock acceleration (DSA) in supernova remnants (SNRs) within the Galaxy. Plasma and MHD simulations have shown that the self-excitation of MHD waves and amplification of magnetic fields via plasma instabilities are an integral part of DSA for strong collisionless shocks. In this study we explore how plasma processes such as plasma instabilities and wave-particle interactions can affect the energy spectra of CR protons and electrons, using time-dependent DSA simulations of SNR shocks. We demonstrate that the time-dependent evolution of the shock dynamics, the self-amplified magnetic fields and $Alfv{\acute{e}nic$ drift govern the highest energy end of the CR energy spectra. As a result, the spectral cutoffs in nonthermal X-ray and ${\gamma}$-ray radiation spectra are regulated by the evolution of the highest energy particles, which are injected at the early phase of SNRs. We also find that the maximum energy of CR protons can be boosted significantly only if the scale height of the magnetic field precursor is long enough to contain the diffusion lengths of the particles of interests. Thus, detailed understandings of nonlinear wave-particle interactions and time-dependent DSA simulations are crucial for understanding the nonthermal radiation from CR acceleration sources.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.05a
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• pp.105-108
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• 2006

This paper describes a new constructing method of multifunctional biosensor using many kinds of biomaterials. A metal particle and an array was fabricated by photolithographic. Biomaterials were immobilized on the metal particle. The array and the particles were mixed in a buffer solution, and were arranged by magnetic force interaction and random fluidic self-assembly. A quarter of total Ni dots were covered by the particles. The binding direction of the particles was controllable, and condition of particles was almost with Au surface on top. The particles were successfully arranged on the array. The biomaterial activities were detected by chemiluminescence and electrochemical methods.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.6
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• pp.615-621
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• 2004

This paper describes a new constructing method of multifunctional biosensor using many kinds of biomaterials. A metal particle and an array was fabricated by photolithographic. Biomaterials were immobilized on the metal particle. The array and the particles were mixed in a buffer solution, and were arranged by magnetic force interaction and random fluidic self-assembly. A quarter of total Ni dots were covered by the particles. The binding direction of the particles was controllable, and condition of particles was almost with Au surface on top. The particles were successfully arranged on the array. The biomaterial activities were detected by chemiluminescence and electrochemical methods.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.160-161
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• 2006

Seasonal changes have been recognized in particle characteristics and forming characteristics of iron powder with insulated coating for a compacted magnetic core because of its high hygroscopicity, due to its phosphate coating and resin binder additives. For this reason, particle characteristics and molding characteristics of the powder with diverse water absorbtivity have been studied. The result shows that the higher the volume of absorbed water, the worse the fluidity becomes, resulting in the reduction in both springback during the molding process and expansion reduction after the heat treatment. The requirement on dimension accuracy for the finished product can be satisfied with an additional drying process on the material powder, which contributes to maintain its water volume constant.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.386-387
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• 2006

This research describes a new constructing method of multifunctional biosensor using many kinds of biomaterials. A metal particle and an array was fabricated by photolithographic. Biomaterials were immobilized on the metal particle. The array and the particles were mixed in a buffer solution, and were arranged by magnetic force interaction and self-assembly. A quarter of total Ni dots were covered by the particles. The binding direction of the particles was controllable, and condition of particles was almost with Au surface on top. The particles were successfully arranged on the array. The biomaterial activities were detected by chemiluminescence and electrochemical methods.