• Steel and Composite Structures
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• 제23권6호
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• pp.691-714
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• 2017

Rotating fluid induced vibration and instability of embedded piezoelectric nano-composite separators subjected to magnetic and electric fields is the main contribution of present work. The separator is modeled with cylindrical shell element and the structural damping effects are considered by Kelvin-Voigt model. Single-walled carbon nanotubes (SWCNTs) are used as reinforcement and effective material properties are obtained by mixture rule. The perturbation velocity potential in conjunction with the linearized Bernoulli formula is used for describing the rotating fluid motion. The orthotropic surrounding elastic medium is considered by spring, damper and shear constants. The governing equations are derived on the bases of classical shell theory (CST), first order shear deformation theory (FSDT) and sinusoidal shear deformation theory (SSDT). The nonlinear frequency and critical angular fluid velocity are calculated by differential quadrature method (DQM). The detailed parametric study is conducted, focusing on the combined effects of the external voltage, magnetic field, visco-Pasternak foundation, structural damping and volume percent of SWCNTs on the stability of structure. The numerical results are validated with other published works as well as comparing results obtained by three theories. Numerical results indicate that with increasing volume fraction of SWCNTs, the frequency and critical angular fluid velocity are increased.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2009년도 춘계학술발표대회
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• pp.7.1-7.1
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• 2009

The use of Duplex stainless steel as a thermo-implant categorizes into two clinical applications: hyperthermia and thermal ablation or destruction. The goal of hyperthermia is to destroy the heat-sensitive abnormal cells and minimize normal cell death maintaining heat between $42^{\circ}C$ and $46^{\circ}C$. Thermal ablation takes place when the local tissue temperature increases greater than $46^{\circ}C$. This elevated temperature denatures protein irreversibly resulting cellular death. The author introduced several thermo-implants such as thermo-rod, thermo-stent, thermo-coil and thermoacupuncture-needle. Those thermo-implants are made of duplex stainless steel which can produce regulated heat by itself within an induction magnetic field. Thermal ablation characteristics of the thermo-rod on tumor hyperthermia depend on configurations of the thermo-rods and the magnitude of the induction magnetic strength. The exothermic properties of the thermo-implants can be characterized using the calorimetric test and the heat affected zone(HAZ) analyses in vitro. Thermal radiation studies using thermo-coils and thermo-stents show the capability of the occlusion of animal blood vessels and inhibiting the proliferation of the abnormal smooth muscle cell growth and inflammatory cell reactions maintaining the heat between $42^{\circ}C$ and $46^{\circ}C$ minimizing a normal cell death in the study on external iliac artery of the New Zealand White (NZW) rabbit. Thermal stimulation study using thermo-acupuncture needles suggests the potential applications of the automated acupunctural therapies.

• Journal of Magnetics
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• 제11권1호
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• pp.55-59
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• 2006

The effect of annealing temperature on the permeability and giant magneto-impedance (GMI) behaviors of $Fe_{68.5}Mn_{5}Si_{13.5}B_9Nb_3Cu_1$ amorphous alloy has been systematically investigated. The nanocrystalline $Fe_{68.5}Mn_{5}Si_{13.5}B_9Nb_3Cu_1$ alloys consisting of ultra-fine $(Fe,Mn)_3Si$ grains embedded in an amorphous matrix were obtained by annealing their precursor alloy at the temperature range from $500^{\circ}C\;to\;600^{\circ}C$ for 1 hour in vacuum. The permeability and GMI profiles were measured as a function of external magnetic field. It was found that the increase of both the permeability and the GMI effect with increasing annealing temperature up to $535^{\circ}C$ was observed and ascribed to the ultrasoft magnetic properties in the sample, whereas an opposite tendency was found when annealed at $600^{\circ}C$ which is due to the microstructural changes caused by high-temperature annealing. The study of temperature dependence on the permeability and GMI effect showed some insights into the nature of the magnetic exchange coupling between nanocrystallized grains through the amorphous boundaries in nanocrystalline magnetic materials.

• 한국자기학회지
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• 제15권2호
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• pp.113-117
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• 2005

4-point focused floating Bone furnace를 이용하여 multiferroic $HoMnO_3$ 단결정을 제조하였으며, 직접합성법으로 $HoMn_{1-x}\;^57Fe_xO_3$ (x=0, 0.01, 0.02, 0.05) 분말 시료를 제조하여 그 결정학적 및 자기적 성질을 연구하였다. 결정구조는 hexagonal 구조로, (110) 방향이 자화용이축 임을 알 수 있었고, 온도 변화에 따른 강유전 상수(dielectric constant $\epsilon$)는 c축과 평행한 방향에서 특이성(anomaly)을 갖는 것으로 나타났다. 이 때 특이성이 나타나는 온도 구간은, c축 방향으로 인가된 자기장 세기에 따라 민감하게 변화함이 관측되고 있어, multiferroic 소자로의 응용 가능성을 제시하고 있다. 한편 Mn 자리에 $^{57}Fe$를 미량 치환한 분말 시료에 대하여 $M\ddot{o}ssbauer$ 분광학적 연구를 수행하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2000년도 제18회 학술발표회 논문개요집
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• pp.163-163
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• 2000

In this research, we used the ion irradiation technique which has an advantae in improving intentionally the properties of surface and interface in a non-equilibrium, instead of the conventional annealing method which has been known to improve the material properties in the equilibrium stat. Cu/Co multilayered films were prepared on SiN4/SiO2/Si substrates by the electron-beam evaporation for the Co layers and the thermal evaporation for the Cu layers in a high vacuum. The ion irradiation with a 80keV Ar+ was carried out at various ion doses in a high vacuum. Hysteresis loops of the films were investigated by magneto-optical polar Kerr spectroscopy at various experimental conditions. The change of atomic structure of the films before and after the ion irradiation was studied by glancing angle x-ray diffraction, and the intermixing between Co and Cu sublayers was confirmed by Rutherford backscattering spectroscopy. The surface roughness and magneto-resistance were measured by atomic force microscopy and with a four-point probe system, respectively. During the magneto-resistance measurement, we changed temperature and the direction of magnetization. From the results of experiments, we found that the change at the interfaces of the Cu/Co multilayered film induced by ion irradiation cause the change of magnetic properties. According to the change in hysteresis loop, the surface inplane component of magnetic easy axis was isotropic before the ion irradiation, but became anisotropic upon irradiation. It was confirmed that this change influences the axial behavior of magneto-resistance. Especially, the magneto-resistance varied in accordance with an external magnetic field and the direction of current, which means that magneto-resistance also shows the uniaxial behavior.

• 한국자기학회지
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• 제18권1호
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• pp.1-8
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• 2008

최근 발전하는 초박막 자기 시료의 정확한 자기 모멘트 측정을 위하여 저자기 모멘트 표준 시료를 제작하였다. 정밀한 저자기 모멘트 표준시료를 제작하기 위해서 자력계를 미리 자기잡음으로부터 차폐시켰고, 시료준비과정에서 강자성 불순물을 고려한 시료의 순도, 절단 방법, 시료의 모양과 두께 등을 고려하였다. 본 연구에서는 SQUID 자력계를 이용한 자기 모멘트 측정에 적합하게 $4mm{\times}6mm$ 면적을 갖는 Al, Ti과 W로 된 판상형 시료 3 개를 준비하였다. Pd 금속의 경우는 이미 잘 보정된 실린더형 시료를 사용하였다. 준비된 세 개의 판상형 시료의 경우 50,000 Oe 이내의 자기장영역에서 자기이력현상이 관측되지 않았고 모두 양호한 선형성을 보였다. 290K에서 310K까지의 온도영역에서 Ti, Al, W의 자기모멘트 값의 변화는 각각 0.7%, 1.5%, 0.1% 이내로 작았다. 본 연구에서 준비된 각각의 시편에 대해 자기모멘트 값을 결정하였으며, round robin test를 통하여 측정값의 신뢰도를 확인하였다. 그 결과 본 연구에서 제작한 표준시료는 저자기 모멘트 측정에 편리하고 적합하게 활용될 수 있음을 알 수 있었다.

• 한국지구과학회:학술대회논문집
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• 한국지구과학회 2010년도 춘계학술발표회 논문집
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• pp.53-53
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• 2010

지표위의 어떤 지점에서의 지구자기의 수평분력 방향과 진북방향 사이의 각을 편각(Declination)이라고 정의한다. 쉽게 말하면 편각은 나침반의 자침이 가러 키는 방향과 진북방향과의 사이 각을 말한다. 대부분의 사람들은 나침반의 자침이 북자기극(North magnetic pole)을 가러킨다고 잘못알고 있다. 지구 다이나모설(Geodynamo theory)에 의하면 주로 철(약 90%)로 구성된 외핵 속에서 계속 생성 유지되고 있는 복잡한 (각각 나선형(helical)의 회전축에 대체로 평행하거나 평행하지 않은) 대류(Convection currents)에 수반하는 전류가 복잡한 지구자기장을 형성한다. 지표상에서 측정한 지구자기장의 자료를 Spherical harmonic analysis 으로 분석하면 한 개의 커다란 쌍극자(Dipole) (Inclined geocentric dipole 또는 주된 자기장(Main field) 이라고 부름), 적도쌍극자(Equatorial dipole), 4극자 (Quadrupoles), 8극자(Octupoles) 등의 여러 개의 크고 작은 쌍극자들의 총합이 지구자기장의 근원인 것처럼 해석되고 있다. 어떤 지점에서의 지구자기장의 방향은 외핵에서 생성된 천체 자기장에서 Main field를 제거한 나머지 자기장과, 상부 맨틀(upper mantle), 지각 및 지표상에 존재하는 인공 물체 또는 암석 및 광석 등의 잔류자기 및 유도자기 그리고 지형 등의 영향으로 결정된다. 어떤 지점에서의 지구자기장의 방향은 태양풍(Solar wind)과 전리층 사이의 상호작용 등의 외부자장(external field)의 영향도 받는다. 비쌍극자 자장(Non-dipole field)은 지표상에서 측정되는 총자기장에서 외핵에서 생성된 주된 자기장(Main field) 즉, 지구의 회전축에서 약 11.5도 기울어진 쌍극자 자장을 제거하고 남는 자기장을 말한다. 따라서 편각은 비쌍극자자장의 영향을 가장 많이 받는다. 비쌍극자 자장은 정지한 상태의 자장(standing field) 과 매년 서쪽으로 약 0.2도 움직이는 Westward drift하는 자장으로 크게 두 가지로 구분된다. 쌍극자 자장의 방향은 매우 느리게 변하지만 그 세기는 현재 비교적으로 빠르게 약해지고 있다. 비교적으로 매우 빠르게 변하는 비쌍극자 자장의 변화를 영년변화(Secular variation) 이라고 한다.

• Journal of Mechanical Science and Technology
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• 제20권4호
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• pp.569-579
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• 2006

In the present study, the unsteady Couette flow with heat transfer of a dusty viscous incompressible electrically conducting fluid under the influence of an exponential decaying pressure gradient is studied without neglecting the Hall effect. The parallel plates are assumed to be porous and subjected to a uniform suction from above and injection from below while the fluid is acted upon by an external uniform magnetic field is applied perpendicular to the plates. The governing equations are solved numerically using finite differences to yield the velocity and temperature distributions for both the fluid and dust particles.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 B
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• pp.909-911
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• 2002

Rises of current level at power applications, such as transformer, motor, power cable need for using stacked HTS tapes. In this paper, we measured rises of temperature and tap voltage in 4-stacked HTS tapes under over-current condition. We measured 4-stacked HTS tapes properties under over-current condition with a little temperature rise as well as a large temperature rise. Rises of temperature and tap voltage are measured by using E-type thermocouples and voltage taps, respectively. According to the results of measurement, rises of tap voltage under over-current condition with a large temperature rises depends on rises of temperature.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1991년도 추계학술대회 논문집 학회본부
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• pp.419-422
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• 1991

A mathematical model was developed to predict the temperature, the density, and the velocity distribution of an inductively coupled thermal plasma. It was for an atmospheric pressure argon thermal plasma generated by a 4 MHz radio frequency power. It has been shown that the hottest region can be moved toward centrial region by applying an external magnetic field. Based on the results of the simulation. an ICP(Inductively Coupled thermal Plasma) system was constructed and thermal plasma was generated.