• 한국전자파학회논문지
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• 제29권3호
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• pp.167-170
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• 2018

MoM은 대표적인 적분방정식기반 full-wave simulation 방법이며, 이는 MLFMM 방법을 적용하여 효율적으로 계산될 수 있다. MoM 또는 MLFMM 방법에서 대규모 산란체 표면전류를 계산하는 과정에는 주로 반복법들이 사용된다. 이 가운데 BiCGstab(l)은 l값이 증가할수록 반복횟수는 줄어들지만, 반복당 수행되는 연산횟수가 증가하는 특징이 있다. 본 논문에서는 MLFMM 방법에 적용된 BiCGstab(l) 반복법의 l값에 따른 수렴속도와 연산량을 분석한 후, 효율적인 l값을 제안한다.

• 한국재료학회지
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• 제19권11호
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• pp.601-606
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• 2009

$BiFeO_3$ (BFO) thin films were prepared on $Pt/TiO_2/Si$ substrate by r.f. magnetron sputtering. The effects of deposition pressure on electrical properties were investigated using measurement of dielectric properties, leakage current and polarization. When BFO targets were prepared, Fe atoms were substituted with Mn 0.05% to increase electrical resistivity of films. (Fe+Mn)/Bi ratio of BFO thin films increases with increasing partial pressure of $O_2$ gas. The deposited films showed the only BFO phase at 10 mTorr, the coexistence of BFO and $Bi_2O_3$ phase at 30-50 mTorr, and the only $Bi_2O_3$ phase at 70 mTorr. The crystallinity of BFO films was reduced due to the higher Bi contents and the decrease of surface mobility of atoms at high temperature. The porosity and surface roughness of films increased with the increase of the deposition pressure. The films deposited at high pressure showed low dielectric constant and high leakage current. The dielectric constant of films deposited at various deposition pressures was 84${\sim}$153 at 1 kHz. The leakage current density of the films deposited at 10${\sim}$70 mTorr was about $7{\times}10.6{\sim}1.5{\times}10.2A/cm^2$ at 100 kV/cm. The leakage current was found to be closely related to the morphology and composition of the BFO films. BFO films showed poor P-E hysteresis loops due to high leakage current.

• 한국광물학회지
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• 제11권2호
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• pp.117-125
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• 1998

Crystallization behavior of platinum minerals within Pt-Sb-Bi bearing ore magmas and mineralogical properties of the existing minerals were investigated at 1,00$0^{\circ}C$ by synthetic experiment. High purity reagents were used as starting materials and silica tubings as containers. Reaction products were analysed by reflecting microscopy, X-ray diffraction, electron probe microanalysis, and micro-hardness test. Stable minerals at 1,00$0^{\circ}C$ are platinum, electron probe microanalysis, and micro-hardness test. Stable minerals at $1,000^{\circ}C$ are platinum, stump-flite (PtSb) and geversite (PtSb2). They are in equilibrium with liquid (ore magma). Platinum contains considerable amount of Sb of 7.5 at.%, whereas Bi only up to 0.9 at.%. Pure stumpflite is hexagonal with space group P63/mmc, and unit cell parameters are a=4.1318(6), c=5.483(1)$\AA$. VHN50=417(2)$\AA$. Geversite has cubic structure with space group Pa3. Cell parameters are a=6.4373(2)$\AA$ and Vicker hardness values VHN50=663.5 (566~766). Both stumpflite and geversite show solid solution and their end-members are Pt48.8Sb40.7-Bi10.5, and Pt33.7-Sb59.8Bi6.5, respectively. Although stumpflite (m.p. $1,043^{\circ}C$) and unnamed PtBi (m.p. 7$65^{\circ}C$) do not form a complete solid solution at $1,000^{\circ}C$, they are known, at $600^{\circ}C$, to form a continuous solid solution. Geversit (m.p. $1,226^{\circ}C$) also forms complete solid solution with insizwaite (m.p. $660^{\circ}C$). Unit cell dimensions of the minerals above increases with the amount of Bi substituting for Sb.

• 마이크로전자및패키징학회지
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• 제18권4호
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• pp.55-61
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• 2011

n형 $Bi_2(Te_{0.9}Se_{0.1})_3$ 분말을 기계적 합금화 공정으로 제조하고 텅스텐 분말을 분산시켜 $550^{\circ}C$에서 30분간 가압소결 후, 텅스텐 함량에 따른 열전특성을 분석하였다. 텅스텐 분말을 분산시키지 않은 $Bi_2(Te_{0.9}Se_{0.1})_3$ 가압소결체의 상온 출력인자는 $21.9{\times}10^{-4}$ $W/m-K^2$ 이었으며, 1 vol% 텅스텐 분말의 분산에 의해 상온 출력인자가 $30.5{\times}10^{-4}$ $W/m-K^2$로 증가하였다. 텅스텐 분말을 분산시키지 않은 $Bi_2(Te_{0.9}Se_{0.1})_3$ 가압소결체는 상온에서 0.52의 무차원 성능지수를 나타내었으며, 1 vol% 텅스텐 분말의 분산에 의해 무차원 성능지수가 0.95로 크게 향상되었다.

• Journal of Magnetics
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• 제14권2호
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• pp.62-65
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• 2009

The multiferroic $BiFeO_3$ has been investigated extensively in both thin film and ceramic form. However, the synthesis of a perfect sample with high resistivity is a prerequisite for examining its properties. This paper reports the synthesis of multiferroic $BiFeO_3$ along with its structural, electrical and magnetic properties in ceramic form. Polycrystalline ceramic samples of $BiFeO_3$ were synthesized by solid-state reaction using high purity oxides and carbonates. The formation of a single-phase compound was confirmed by x-ray diffraction and its lattice parameters were determined using a standard computer program. The microstructural studies and density measurement confirmed that the prepared samples were sufficiently dense for an examination of its electrical and magnetic properties. The dc electrical conductivity studies show that the sample was resistive with an activation energy of ${\sim}0.81\;eV$. The magnetization measurement showed a linear ($M{\sim}H$) curve indicating antiferromagnetic characteristics.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.450.1-450.1
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• 2014

열에너지를 전기에너지로 변환하거나 또는 전기에너지를 열에너지로 직접 변환하는 열전 변환 기술이 주목받고 있다. 열전 변환 효율은 성능지수($ZT={\alpha}^2{\sigma}T{\kappa}^{-1}$)로 평가되며, 여기서 ${\alpha}$, ${\sigma}$, ${\kappa}$, T는 각각 열전재료의 제벡계수, 전기전도도, 열전도도 및 절대온도이다. 따라서 우수한 열전재료는 높은 제벡계수와 전기전도도 그리고 낮은 열전도도를 가져야 한다. Bismuth telluride는 상온영역에서 성능지수가 높은 재료로서, $Bi_2Te_3$에 $Bi_2Se_3$와 고용체를 형성하면 원자의 치환으로 포논산란에 의해 열전도도가 낮아지고, 도핑으로 전기적 특성을 조절하여 성능지수를 향상시킬 수 있다. 본 연구에서는 진공밀폐 용해법으로 $Bi_2Te_{2.85}Se_{0.15}:I_m$ (m=0.0~0.045) 고용체를 합성하여 상분석을 실시하고, 전자 이동특성 및 열전 특성을 평가하였다.

• Progress in Superconductivity
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• 제3권2호
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• pp.247-251
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• 2002

In general, the bubbling, generated during the fabrication of the tapes, breaks the superconducting filament, and critical current of the tapes will be decreased. Heat-treatment schemes of Bi-2223/Ag HTS tapes were modified, such as pre-annealing of multi-stacked billet, 2-step main sintering and ramp rate etc. The generation of bubbling was drastically decreased from 20 bubbles/m to 0 ~ 1 bubble/m by the modified heat-treatment. Therefore, the value of critical current of the tapes without bubbling was increased almost twice higher than that of already existing tapes. Critical current up to 42 A in 40 m length Bi-22231Ag tapes have been measured at 77K, self-field, 1$mutextrm{V}$/cm criterion. It could be confirmed that elimination of bubbling is effective to maintain the superconducting property along the tape length.

• 한국표면공학회지
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• 제39권2호
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• pp.57-63
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• 2006

In this study, In-base solder was applied to the interface between $Bi_2Sr_2Ca_1Cu_2O_x(Bi_{2212})$ superconductor and Cu-Ni shunt metal at the temperature lower than $150^{\circ}C$. Most of the cases, $Bi_{2212}$ superconductor was precoated with Ag by electroplating in order to improve the contact properties of the solder layer. When the superconductor was directly soldered on to the superconductor, the solder was easily separated without external force. The shear strength of the contact between superconductor and shunt metal increased from 69.2 kgf to 74.4 kgf and 80.1 kgf, as the current density of the Ag electroplating was changed from 63 mA to 96 mA and 126 mA, respectively. The contact strength also increased to 49.9 kgf and 69.2 kgf when thickness of the electroplated Ag layer increased to $5{\mu}m$ and $10{\mu}m$, reapectively.

• Kyungpook Mathematical Journal
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• 제56권1호
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• pp.83-94
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• 2016

Let M and N be modules over a ring R. The purpose of this paper is to study modules M, N for which the bi-module [M, N] is regular or pi. It is proved that the bi-module [M, N] is regular if and only if a module N is semi M-projective and $Im({\alpha}){\subseteq}^{\oplus}N$ for all ${\alpha}{\in}[M,N]$, if and only if a module M is semi N-injective and $Ker({\alpha}){\subseteq}^{\oplus}N$ for all ${\alpha}{\in}[M,N]$. Also, it is proved that the bi-module [M, N] is pi if and only if a module N is direct M-projective and for any ${\alpha}{\in}[M,N]$ there exists ${\beta}{\in}[M,N]$ such that $Im({\alpha}{\beta}){\subseteq}^{\oplus}N$, if and only if a module M is direct N-injective and for any ${\alpha}{\in}[M,N]$ there exists ${\beta}{\in}[M,N]$ such that $Ker({\beta}{\alpha}){\subseteq}^{\oplus}M$. The relationship between the Jacobson radical and the (co)singular ideal of [M, N] is described.

• Journal of Magnetics
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• 제21권2호
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• pp.179-182
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• 2016

In this paper, 10 nm $Fe_3O_4$ nanoparticles were modified on the surface of $2{\mu}m$ flower-like bismuth oxychloride (BiOCl) spheres by a facile co-precipitation method. The results showed that the $Fe_3O_4/BiOCl$ nanocomposites exhibited excellent photocatalytic activity and superparamagnetic property ($M_s=3.22emu/g$) under visible light for Rhodamine B (RhB) degradation. Moreover, the $Fe_3O_4-BiOCl$ photocatalyst possessed magnetic recyclable property, which could maintain high photocatalytic effective even after 20 cycle times. These characteristic indicates a promising application for wastewater treatment.