• 터널과지하공간
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• 제12권3호
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• pp.171-178
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• 2002

본 연구에서는 마제형터널 주변에 공동이 존재하는 경우에 대해 동적해석을 수행함으로써 터널주변의 공동이 터널의 동적거동에 미치는 영향을 검토하였다. 이를 위해 반무한 평면상에서 터널의 동적응답해석을 수행할 수 있는 해석기법을 개발하였다. 먼저 주파수 영역에서의 다층 반무한 지반내에서의 동적 기본해를 유도하였고 이를 경계요소에 적용하였다. 외부영역을 모형화한 경계요소를 내부영역의 유한요소와 조합하여 반무한 영역에서의 터널구조의 동적응답을 구할 수 있도록 하였다. 개발된 기법의 검증을 위하여 단층 및 다층 반무한 구조계에 대해 Ricker 파형을 이용한 동적해석을 수행하여 기존의 해석결과와 비교하였고, 개발된 기법을 이용하여 석회암층에 있는 터널에 대해 공동의 유무 및 터널과의 이격거리에 따른 터널의 동적거동을 고찰하였다.

• Bulletin of the Korean Chemical Society
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• 제35권2호
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• pp.494-500
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• 2014

Indium-doped zinc oxide nanocrystals (IZO NCs), capped with stearic acid (SA) of different sizes, were synthesized using a hot injection method in a noncoordinating solvent 1-octadecene (ODE). The ligand exchange process was employed to modify the surface of IZO NCs by replacing the longer-chain ligand of stearic acid with the shorter-chain ligand of butylamine (BA). It should be noted that the ligand-exchange percentage was observed to be 75%. The change of particle size, morphology, and crystal structures were obtained using a field emission scanning electron microscope (FE-SEM) and X-ray diffraction pattern results. In our study, the 5 nm and 10 nm IZO NCs capped with stearic acid (SA-IZO) were ligand-exchanged with butylamine (BA), and were then spin-coated on a thermal oxide ($SiO_2$) gate insulator to fabricate a thin film transistor (TFT) device. The films were then annealed at various temperatures: $350^{\circ}C$, $400^{\circ}C$, $500^{\circ}C$, and $600^{\circ}C$. All samples showed semiconducting behavior and exhibited n-channel TFT. Curing temperature dependent on mobility was observed. Interestingly, mobility decreases with the increasing size of NCs from 5 to 10 nm. Miller-Abrahams hopping formalism was employed to explain the hopping mechanism insight our IZO NC films. By focusing on the effect of size, different curing temperatures, electron coupling, tunneling rate, and inter-NC separation, we found that the decrease in electron mobility for larger NCs was due to smaller electronic coupling.

• 한국정밀공학회지
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• 제13권3호
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• pp.110-122
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• 1996

Finite element analysis tool was developed to analyze the casting process. Generally, casting process consists of mold filling and solidification. Both filling and solidication process were simulated simultaneously to investigate the effects of process variables and to predict the defect. At filling process, thermal coupling was especially considered to investigate thermal history of material during the filling stage. And thermal condition at the final stage of filling is used as the initial conditions in a solidification process for the exact simullation of the actual casting processes. At mold filling process, Lagragian-type finite element method with automatic remeshing scheme was used to find the material flow. A perturbation method with artificial viscosity is adopted to avoid numerical instability in low viscous fluid. At solidification process, enthalpy-based finite element method was used to solove the heat transfer problem with phase change. And elastic stress analysis has been performed to predict the thermal residual stress. Through the FE analysis, solidification time, position of solidus line, liquidus line and thermal residual stress are found. Through the study, the importance of combined analysis has been emphasized. Finite element tools developed in this study will be used process design of casting process and may be basic structure for total CAE system of castings which will be constructed afterward.

• JSTS:Journal of Semiconductor Technology and Science
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• 제8권2호
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• pp.128-133
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• 2008

Phase-change random access memory (PRAM) chip cell phase of amorphous state is rapidly changed to crystal state above 160 Celsius degree within several seconds during Infrared (IR) reflow. Thus, on-board programming method is considered for PRAM chip programming. We demonstrated the functional 512Mb PRAM with 90nm technology using several novel core circuits, such as metal-2 line based global row decoding scheme, PN-diode cells based BL discharge (BLDIS) scheme, and PMOS switch based column decoding scheme. The reverse-state standby current of each PRAM cell is near 10 pA range. The total leak current of 512Mb PRAM chip in standby mode on discharging state can be more than 5 mA. Thus in the proposed BLDIS control, all bitlines (BLs) are in floating state in standby mode, then in active mode, the activated BLs are discharged to low level in the early timing of the active period by the short pulse BLDIS control timing operation. In the conventional sense amplifier, the simultaneous switching activation timing operation invokes the large coupling noise between the VSAREF node and the inner amplification nodes of the sense amplifiers. The coupling noise at VSAREF degrades the sensing voltage margin of the conventional sense amplifier. The merit of the proposed sense amplifier is almost removing the coupling noise at VSAREF from sharing with other sense amplifiers.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2002년도 추계 학술발표회 논문집
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• pp.106-113
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• 2002

In this study, a numerical analysis method for soil-pile interaction in frequency domain problem is presented. The total soil-pile interaction system is divided into two parts so called near field and far field. In the near field, beam elements are used for a pile and plain strain finite elements for soil. In the far field, dynamic fundamental solution for multi-layered half planes based on boundary element formulation is adopted for soil. These two fields are coupled using FE-BE coupling technique In order to verify the proposed soil-pile interaction analysis, the dynamic responses of pile on multi-layered half planes are simulated and the results are compared with the experimental results. Also, the dynamic response analyses of interface spring elements are performed. As a result, less spring stiffness makes the natural frequency decrease and the resonant amplitude increase.

• 한국지진공학회논문집
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• 제5권2호
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• pp.83-91
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• 2001

본 연구에서는 2차원 평면상에서 자유장응답 해석을 위하여 유한요소-경계요소 조합에 의한 수치해석기법을 개발하였다. 전체 계를 외부영역과 내부영역으로 구분하였다. 외부영역은 동적 다층반무한 기본해를 이용한 경계요소로 모형화되고 내부영역은 유한요소로 모형화하여 조합하였다. 다층지반의 외부에서 입사하는 지진에 의한 지진응답해석을 수행하기 위하여 동적기본해를 이용한 자유장응답해석을 수행하였다. 지진응답해석에서는 지반의 전단병형률에 따라 변화하는 비선형특성을 모형화하기 위해 등가선형화기법을 적용하였다. 지진응답해석의 검증에 의하여 해석결과를 상용프로그램의 결과와 비교하였다. 결과적으로 지진응답해석을 효과적으로 수행할 수 있는 수치해석기법을 개발하였고 구조물이 있는 경우로의 확장돠 가능하게 되었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.122-125
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• 2006

The Substructure Synthesis means the technology to predict the dynamic properties of an assembly from the properties of its components, or to predict the effect of a modification on a structure. The FRF Based Substructuring method is a kind of the Substructure Synthesis and very useful to predict the efficiency of the product in the early stage of development. Especially, the Hybrid FBS method is very useful to predict the vehicle NVH characteristics after modifying some components of the vehicle. Target components can be established on the basis of test models and FE models of the prototype constructed in the early stage of development. In this study, the Hybrid FBS method was applied to vehicle subframe and car-body in order to reduce vehicle interior noise induced by engine exciting force.

• 한국자기학회지
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• 제10권2호
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• pp.62-66
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• 2000

비자성사이층 Cu 두께(30 $\AA$, 35 $\AA$, 40 $\AA$)를 달리한 glass(7059)/N $i_{81}$$Fe_{19}$(70 $\AA$)/Co(10 $\AA$)/Cu(t $\AA$)/Co(15 $\AA$)/N $i_{81}$$Fe_{19}$(35 $\AA$)N $i_{25}$M $n_{75}$(250 $\AA$)Ta(50 $\AA$) 스핀밸브박막(spin valve film; SVF) 을 dc 스퍼터링으로 제작하였다 이 시편을 진공 열처리 한 후 자유자성층의 상호결합세기(interlayer coupling field; $H_{inf}$ )와 보자력(coercivity; $H_{sf}$ )에 대한 열처리 순환횟수 및 비자성층 두께 의존성에 관련한 자기저항특성을 조사했다. Cu 두께가 35 $\AA$인 SVF의 경우에 교환결합세기(exchange coupling field; $H_{ex}$)가 620 Oe, 보자력( $H_{c}$)이 280 Oe 및 자기저항(magnetoresistance; MR)비가 2.5%를 보였다. $H_{inf}$ 와 $H_{cf}$ 는 모든 SVF가 열처리 순환 횟수에 따라 증가하는 경향을 보이다가 일정한 값으로 안정화되며 Cu 35 $\AA$인 경우는 열처리 순환 횟수 15회 이후에 각각 120 Oe 및 75 Oe를 유지한다. $H_{inf}$ 및 $H_{cf}$ 가 열처리 순환횟수 증가에 따라 증가하는 것은 열처리 효과에 의해 Cu층과 Co층의 계면섞임 증대에 의한 유효한 Cu층 두께 감소에 기인한다. Cu가 적정둘레 35 $\AA$ 보다 더 얇아지거나 두꺼워지면 계면섞임에 의한 효과는 각각 더 증대하거나 둔화되는 것으로 분석된다.으로 분석된다..

• 한국소음진동공학회논문집
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• 제13권8호
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• pp.598-604
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• 2003

In this paper a general solution method is presented to obtain the unbalance response orbit from the finite element based equations of motion of a gear-coupled two-shaft rotor-bearing system, whose shafts rotate at their different speeds from each other. Particularly, are proposed analytical solutions of the maximum and minimum radii of the orbit. The method has been applied to analyze the unbalance response of a 800 refrigeration-ton turbo-chiller rotor-bearing system having a bull-pinion speed increasing gear. Bumps in the unbalance response of the driven high speed compressor rotor system have been observed at the first torsional natural frequency due to the coupling effect of lateral and torsional dynamics. Further, the proposed analytical solutions have agreed well with those obtained by a full numerical approach. The proposed analytical solutions can be generally applied to obtain the maximum and minimum radii of the unbalance response orbits of dual-shaft rotor-bearing systems coupled by bearings as well.

• 한국자기학회지
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• 제5권5호
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• pp.366-371
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• 1995

High performance magnetic materials are characterized by the combination of outstanding magnetic properties and optimized microstructures, e.g., nanocrystalline composites of multilayers and small particle systems. The characteristic parameters of the hysteresis loops of these materials vary over more than a factor of $10^{6}$ with optimum values for the coercive field of several Tesla and permeabilities of $10^{6}$. Within the framework of the computational micromagnetism (nanomagnetism) using the finite element method the upper and lower bounds of the coercive field of different types of grain ensembles and multilayers have been determined. For the case of nanocrystalline composites the role of grain size, exchange and dipolar coupling between grains and the degree of grain alignment will be discusses in detail. It is shown that the largest coercivities are obtained for exchange decoupled grains, whereas remanence enhancing requires exchange coupled grains below 20 nm. For composite permanent magnets based on $Nd_{2}Fe_{14}B$ with an amount of ~ 50% soft $\alpha$-Fe-phase coercivities of ${\mu}_{0}H_{c}=0.75\;T$, a remanence of 1.5 T and an energy product of $400\;kJ/m^{3}$ is expected. In nanocrystalline systems the temperature dependence of the coercivity is well described by the relation ${\mu}_{0}H_{c}=(2\;K_{1}/M_{s}){\alpha}-N_{eff}{\mu}_{0}M_{s}$, where the microstructural parameters $\alpha$ and $N_{eff}$ take care of the short-range perturbations of the anisotropy and $N_{eff}$ is related to the long-range dipolar interactions. $N_{eff}$ is found to follow a logarithmic grain size size dependence ${\mu}_{0}H_{c}=(2\;K_{1}/M_{s}){\alpha}-N_{eff}(\beta1nD){\mu}_{0}M_{s}$. Several trends how to achieve the ideal situation $\alpha$->1 and $N_{eff}$->1->0 will be discussed.