• 한국소음진동공학회논문집
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• 제22권6호
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• pp.582-587
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• 2012

This paper presents a solution of the vibration reduction in the hollow shafts by using magentorehological( MR) elastomer. Proposed active damping structure is built by embedding the MR elastomers whose elastic modulus is controllable by an applied magnetic field. MR elastomers consist of synthetic rubber filled with micron-sized magnetizable particles. For reduction of vibration, dynamic damper of hollow shaft is designed by using MR elastomer and equipped in the hollow shaft for the application to drive shaft. Experiment results are shown through the experiments to confirm the effect of MR elastomer dynamic damper for vibration reduction. Thus, the designed damping structure can be applied to vibration absorber used in drive shafts as well as the propeller shafts.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.484-487
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• 2005

In order to get the surface characteristics of the HDI of HDD, the surface damage mechanisms must be totally understood. Particle contamination in hard disk drives is a big concern in today's magnetic recording industry since they are major sources of reliability problems. Namely upon contact with the slider or a contaminant particle, the disk may be scratched or the particles may be embedded into the disk surface. In this work, comparison of scratches was made between those found on actual hard disks and those created using a scratch tester. It was found that ramp loading method is an effective way to make similar scratches as the actual ones. From the ramp loading condition, the relationship between the pressure and the scratch track width could be identified.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.557-560
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• 2008

A two-dimensional particle-in-cell(PIC) simulation with a Monte-Carlo Collision(MCC) has been developed to investigate the discharge characteristics of the acceleration channel of a HET. The dynamics of electrons and ions are treated with PIC method at the time scale of electrons in order to investigate the particle transport. The densities of charged particles are coupled with Poisson's equation. Xenon neutrals are injected from the anode and experience elastic, excitation, and ionization collisions with electrons, and are scattered by ions. These collisions are simulated by using an MCC model. The effects of control parameters such as magnetic field profile, electron current density, and the applied voltage have been investigated. The secondary electron emission on the dielectric surface is also considered.

• 천문학회보
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• 제44권1호
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• pp.50.1-50.1
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• 2019

In coronagraph images, it is often observed that two successive CMEs merge into one another and form complex structures. This phenomenon, so called CME cannibalism caused by the differences in ejecting times and propagating velocities, can significantly degrade forecast capability of space weather, especially if it occur near the Earth. Regarding this, we attempt to analyze the cases that two CMEs are expecting to meet around 1 AU based on their arrival times. For this, we select 13 CME-CME pairs detected by ACE, Wind and/or STEREO-A/B. We find that 8 CME-CME pairs show a shock structure, which means they already met and became one structure. Meanwhile 5 pairs clearly show magnetic holes between two respective shock structures. Based on detailed investigation for each pair and statistical analysis for all events, we can get clues for following questions: 1) How does the solar wind structure change when they are merging? 2) Are there any systematic characteristics of merging process according to the CME properties? 3) Is the merging process associated with the occurrence of energetic storm particles? 4) What causes errors in calculating CME arrival times? Our results and discussions can be helpful to understand energetic phenomena not only close to the Sun but also near the Earth.

• 대한금속재료학회지
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• 제49권1호
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• pp.46-51
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• 2011

Real-time formation of $L1_0$ phase of FePt nanoparticles in the gas phase during ultrasonic-spray pyrolysis is first discussed in the present study. Without any post heat treatment, $L1_0$ phase of FePt nanoparticles appeared at the temperature above $900^{\circ}C$ in the gas phase synthesis. X-ray diffractometry (XRD) and transmission electron microscopy (TEM) studies revealed that FePt nanoparticles less than 10 nm in size contained small volume of $L1_0$ fct phase. However, in other samples obtained at the temperature below $900^{\circ}C$, iron oxide phase co-existed and no evidence of phase transformation was found. Thus, it is anticipated that the time of flight of particles required for crystallization and phase transformation was extended according to the increase of the collision rate. Finally, magnetic properties represented by coercivity and saturation magnetization and functional groups on the particle surface were discussed based on VSM and FT-IR results.

• 한국재료학회지
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• 제31권12호
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• pp.677-681
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• 2021

The Mn-Zn ferrite powders were prepared by high energy ball milling, then compacted and sintered at various temperatures to assess their sintering behavior and magnetic properties. The initial ferrite powders were spherical in shape with the size of approximately 70 ㎛. After 3 h of ball milling at 300 rpm, aggregated powders ~230 nm in size and composed of ~15 nm nanoparticles were formed. The milled powders had a density of ~70 % when compacted at 490 MPa for 3 min. In the samples subsequently sintered at 1,273 K ~ 1,673 K for 3 h, the MnZnFe₂O₄ phase was detected. The density of the sintered samples had a tendency to increase with increasing sintering temperature up to 1,473 K, which produced the highest density of 98 %. On the other hand, the sample sintered at 1,373 K had the highest micro-hardness of approximately 610 Hv, which is due to much finer grains.

• 대한방사성의약품학회지
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• 제8권2호
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• pp.113-118
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• 2022

Gadolinium neutron capture therapy (Gd-NCT) is a precision radiation therapy that kills cancer cells using the neutron capture reaction that occurs when ¹⁵⁷Gd hits thermal neutrons. ¹⁵⁷Gd has the highest thermal neutron capture cross section of 254,000 barns among stable isotopes in the periodic table. Another stable isotope, ¹⁵⁵Gd, also has a high thermal neutron trapping area (~ 60,700 barns), so gadolinium that exists in nature can be used as a Gd-NCT drug. Gd-NCT is a mixed kinetic energy of low-energy and high-energy ionizing particles, which can be uniformly distributed throughout the tumor tissue, thereby solving the disadvantage of heterogeneous dose distribution in tumor tissue. The Gd complexes of small-sized molecule are widely used as contrast agents for magnetic resonance imaging (MRI) in clinical practice. Therefore, these compounds can be used not only for diagnosis but also therapy when considering the concept of Gd-NCT. This multifunctional trial can look forward to new medical advance into NCT clinical practices. In this review, we introduce gadolinium compounds suitable for Gd-NCT and describe the necessity of image guided Gd-NCT.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2003년도 춘계학술발표강연 및 논문개요집
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• pp.44-44
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• 2003

Growth mechanism of carbon nanotubes(CNTs) synthesized by chemical vapor deposition is abided by two growth modes. These growth modes are classified by the position of activated catalytic metal particle in the CNTs. Growth mode can be also affected by interaction between substrate and catalytic metal and induced energy such as thermal and plasma. We studied the reaction of catalytic metal to the substrate and growth mode of CNTs. Various substrates such as Si(100), graphite plate, coming glass, sapphire and AAO membrane are used to study the relation between catalytic metal and substrate in the synthesis of CNTs. For catalytic metal, thin film was deposited on various substrate via sputtering technique with a thickness of ∼20nm and magnetic fluids with none-sized particles were dispersed on AAO membrane. After laying process on AAO membrane, it was dried at 80$^{\circ}C$ for 8 hour. Synthesizing of CNTs was carried out at 900$^{\circ}C$ in NH3/C2H2 mixture gases flow for 10minutes.

• 천문학회보
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• 제46권1호
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• pp.44.1-44.1
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• 2021

한기로 나누어 보면, 흑점의 관측 빈도는 두 기간에서 비슷하지만, 오로라는 냉한기에 집중적으로 관측된다. 특이하게도, 크기가 큰 흑점의 경우는 냉한기보다 온난기에서 관측 빈도가 세 배 이상 높다. 또한, 흑점과 관련된 오로라의 강도를 분석해보면 크기가 큰 흑점은 작은 흑점보다 2~3배 이상 지구영향성이 높다는 것을 알 수 있다.

• 한국자기학회지
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• 제13권1호
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• pp.1-5
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• 2003

조성비에 따른 (CoFe$_2$O$_4$)$_{1-x}$(Y$_3$Fe$_{5}$O$_{12}$)$_{x}$계의 분말을 산화물 합성법에 의하여 제작하였다. 120$0^{\circ}C$의 열처리로 합성된 분말을 X-선 회절기(XRD)로 측정한 결과에 의하면, 시료의 XRD 모형이 garnet과 Co 페라이트로 발생하는 peak으로 이루어짐을 확인할 수 있었다. 또한 주사전자현미경(SEM)을 이용하여 관측한 결과로 구조가 다른 두 개의 철산화물이 하나의 큰 입자로 결합되어 있음을 알 수 있었다. 두 개의 페라이트를 정확히 구분할 수는 없었으나, 구조가 다른 두 개의 페라이트가 하나의 입자로 잘 결합한 것을 확인할 수 있었다. Mossbauer분광기를 이용하여 측정한 결과는 garnet과 Co 페라이트에 의한 specturm의 면적비가 대부분의 흡수 spectrum을 이루고 있으나, 혼합물에 garnet과 Co 페라이트의 양이 충분한 경우에는 garnet에 있는 Fe 이온이 Co 페라이트의 다른 이온들과의 상호작용으로 d-site에 위치하는 흡수 spectrum이 두 개의 sub-spectrum으로 분리되는 것을 확인할 수 있었다. 이러한 결과는 XRD나 SEM의 관측결과와 같이 두 개의 시료가 하나의 입자로 잘 결합하였음을 의미하여, garnet의 철 이온이 Co페라이트의 이온과 상호작용으로 발생한 것이다. 섭동시료자화기(VSM)를 이용하여 측정한 조성비에 따른 시료의 포화자화 측정결과와 이론적으로 계산한 결과가 일치함을 알 수 있었다.