• 한국자기공명학회논문지
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• 제22권4호
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• pp.101-106
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• 2018

Magnetite is the oldest magnet material known to mankind. It is getting attention again from solid state physics researchers now a days because it is one of the most strongly correlated electron systems. Spin, charge, and orbital orders are interplaying with lattice and involved in the Verwey transition where magnetization, conductivity, and structure changes suddenly. The peculiar ordering states above and below the transition temperature mainly originate from the coexistence of $Fe^{2+}$ and $Fe^{3+}$ ions in the B site of the inverse spinel structure. In particular, the state of the charge and orbital order was the oldest and most intriguing problem. NMR has made significant contribution to the investigation of this question. A. Abragam stated that there is no doubt that NMR is a very powerful tool for the study of ferromagnetic and antiferromagnetic materials. In this mini-review, a short history of NMR investigation of magnetite is presented, providing a support to Abragam's claim.

• Computers and Concrete
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• 제23권6호
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• pp.399-408
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• 2019

Structural health monitoring is important for the safety of lives and asset management. In this study, numerical models were developed for the piezoresistive behavior of smart concrete based on finite element (FE) method. Finite element models were calibrated with experimental data collected from compression test. The compression test was performed on smart concrete cube specimens with 75 mm dimensions. Smart concrete was made of cement CEM II 42.5 R, silica fume, fine and coarse crushed limestone aggregates, brass fibers and plasticizer. During the compression test, electrical resistance change and compressive strain measurements were conducted simultaneously. Smart concrete had a strong linear relationship between strain and electrical resistance change due to its piezoresistive function. The piezoresistivity of the smart concrete was modeled by FE method. Twenty-noded solid brick elements were used to model the smart concrete specimens in the finite element platform of Ansys. The numerical results were determined for strain induced resistivity change. The electrical resistivity of simulated smart concrete decreased with applied strain, as found in experimental investigation. The numerical findings are in good agreement with the experimental results.

• 전기전자학회논문지
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• 제22권1호
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• pp.209-212
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• 2018

본 논문에서는 P(VDF-TrFE)유기물 강유전체 기반 metal-ferroelectric-metal (MFM) capacitor 와 차세대 반도체 물질인 질화갈륨 반도체를 활용한 네거티브 커패시턴스 전계효과 트랜지스터를 제작 및 분석 하였다. 27 nm의 두께의 P(VDF-TrFE) MFM 커패시터의 분극지수는 4 MV/cm에서 $6{\mu}C/cm^2$ 값을 나타내었으며 약 65 ~ 95 pF의 커패시턴스 값을 나타내었다. 강유전체의 커패시턴스와 전계효과 트랜지스터의 커패시턴스 매칭을 분석하기 위해 제작된 P(VDF-TrFE) MFM 커패시터는 GaN 전계효과 트랜지스터의 게이트 전극에 집적화 되었으며 집적화되기 전 104 mV/dec 의 문턱전압 이하 기울기에서 82 mV/dec 값으로 개선된 효과를 보였다.

• Journal of Pharmaceutical Investigation
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• 제24권3호spc1호
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• pp.11-18
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• 1994

We have studied the iron uptake by the purified brush-border membrane vesicles (BBMVs) to determine the effect of fructose on the absorption of iron. BBMVs were prepared by the modified calcium precipitation method, The degree of purification was routinely assessed by the marker enzyme, alkaline phosphatase, and the functional integrity was tested by $D-[1-^3H]glucose$ uptake. The appearance of membrane vesicles was shown by transmission electron microscopy (TEM). The uptakes of complexes of labeled iron $[^{59}Fe]$ with fructose and ascorbate were measured with a rapid filtration technique, The uptake rate and pattern of the two iron-complexes, Fe(III)-fructose and Fe(III)-ascorbate, were also observed. A typical overshooting uptake of D-glucose was observed with peak value of $2{\sim}3$ times higher concentration than that at equilibrium. This result was similar to other studies with BBMVs. TEM showed that the size of BBMVs was uniform and we can hardly find any contaminants, Fe(III)-fructose has the higher value of $V_{max}$ and the lower value of Km than those of Fe(III)-ascorbate, respectively. It may be concluded that D-fructose is more effective in promoting the iron absorption than ascorbate.

• Applied Microscopy
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• 제25권3호
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• pp.90-98
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• 1995

In the Fe-Si system, a mixture of a($Fe_{2}Si_5$) - and ${\epsilon}$(FeSi)-composition powders was sintered and heat-treated subsequently at various temperatures and time to get thermoelectric ${\beta}$-phase($FeSi_2$) compacts. The different transformational sequences depending on the heat treating temperature were found through the investigation into phase transformation and microstructural development. That is, a rapid eutectoid decomposition of ${\alpha}{\to}{\beta}+Si$ occurred together with a accompanying slow reaction between the dispersed Si formed by above decomposition and the preexisted ${\epsilon}$ phase at temperatures below $830^{\circ}C$. The unreacted Si and the micropores formed due to the density change upon the transformation coarsened as heat treating time elapsed. At temperatures above $880^{\circ}C$, however, transformation was proceeded by a peritectoid reaction of ${\alpha}+{\epsilon}{\to}{\beta}$. It took at least 200min. to achieve 90% volume fracion of transformed ${\beta}$ phase, and the growth of micro-pores was also observed in this transformational sequence with prolonged heat treating time.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.53-53
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• 2010

Car industry has required light-weight steels, but still with strong mechanical strength. To meet this requirement, a variety of researches on Fe-Al alloys have been performed. As Al is being added in a disordered manner, alloys become more ductile and show higher yield stress. At a certain concentration of Al, however, the Fe-Al alloy system falls in a second phase whose mechanical strength is worsened. To understand the microscopic role of Al, we investigate the stability and the elastic properties of various Fe-Al alloys using ab initio density functional theory. At agiven Al concentration, the equilibrium geometry is obtained among several disordered Fe-Al alloy structures by performing the geometry relaxation. The formation energies and elastic properties such as bulk moduli of the equilibrium structures are also computed as a function of Al concentration. We also investigate the effects of different elements such as Si and Mn. Fe-Si alloy systems exhibit unusual mechanical behaviors requiring further investigation to understand their physical origin. Especially, the microscopic role of Mn is investigated to find its physical origin of preventing the Fe-Al alloy system from forming an unfavorable second phase. The effect of manganese on mechanical properties of Fe-based alloys is also explored.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2012년도 춘계학술대회 논문집
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• pp.777-778
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• 2012

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2014년도 임시총회 및 하계학술연구발표회
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• pp.88-89
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• 2014

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2015년도 자성 및 자성재료 국제학술대회
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• pp.72-72
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• 2015

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2008년도 Asian Magnetics Conference
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• pp.233.2-233.2
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• 2008