• Nuclear Engineering and Technology
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• 제39권5호
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• pp.627-636
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• 2007

The present work is aimed at further discussing the effectiveness of dimensionless parameters recently proposed for the analysis of flow stability in heated channels with supercritical fluids. In this purpose, after presenting the main motivations for the introduction of these parameters in place of previously proposed ones, additional information on the theoretical bases and on the consequences of this development is provided. Stability maps, generated by an in-house program adapted from a previous application to boiling channels, are also shown for different combinations of the operating parameters. The maps are obtained as contour plots of an amplification parameter obtained from numerical discretization and subsequent linearization of governing equations; as such, they provide a quantitatively clear perspective of the effect of different boundary conditions on the stability of heated channels with supercritical fluids. In order to assess the validity of the assumptions at the basis of the in-house model, supporting calculations have been performed making use of the RELAP5/MOD3.3 computer code, detecting the values of the dimensionless parameters at the threshold for the occurrence of instability for a heated channel representative of SCWR proposed core configurations. The obtained results show reasonable agreement with the maps, supporting the applicability of the proposed scaling parameters for describing the dynamic behaviour of heated channels with supercritical fluids.

• Nuclear Engineering and Technology
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• 제10권2호
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• pp.65-72
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• 1978

원자로 가동시, 정상상태에서 벗어나 갑작스럽게 출력이 바뀔 때 발생하는 응력의 집중과 핵 분열시 발생하는 요오드의 부식에 의해서 생기는 피복물질의 응력 부식파괴현상을 이해하기 위하여, 이번 실험에서는 지르칼로이-4(Zicaloy-4)관을 사용하여 요오드응력부식 실험을 원자로 안의 상태에 가깝도록 30$0^{\circ}C$의 상태아래서 행하였다. 요오드 농도에 따라서 지르칼로이-4, 관(Tube)의 응력부식에 한 파괴시간을 구했고, 응력부식을 일으킬 수 있는 임계요오드 농도 및 임계접선방향의 응력을 구하였다. 요오드에 의한 응력부식이 화학석인 반응이라기 보다는 기계적인 반응성격을 갖기 때문에 응력부식을 파괴 역학적인 관점에서 설명하고자 응력과 파괴시간을 함수관계로 다음과 같이 표시해 보았다. log t$_{F}$ =5.5- (3/2) log$_{c}$-4log$\sigma$ t$_{F}$ : 파괴시간(") c : 요오드농도(mg/㎤) $\sigma$ : 응력 ($10^4$psi).

• Journal of Magnetics
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• 제6권4호
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• pp.132-141
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• 2001

The switching characteristics and the magnetization-flop behavior in magnetic tunnel junctions exchange biased by synthetic antiferromagnets (SyAFs) are investigated by using a computer simulations based on a single-domain multilayer model. The bias field acting on the free layer is found to be sensitive to the thickness of neighboring layers, and the thickness dependence of the bias field is greater at smaller cell dimensions due to larger magnetostatic interactions. The resistance to magnetization flop increases with decreasing cell size due to increased shape anisotropy. When the cell dimensions are small and the synthetic antiferromagnet is weakly, or not pinned, the magnetization directions of the two layers sandwiching the insulating layer are aligned antiparallel due to a strong magnetostatic interaction, resulting in an abnormal magneto resistance (MR) change from the high-MR state to zero, irrespective of the direction of the free-layer switching. The threshold field for magnetization-flop is found to increase linearly with increasing antiferromagnetic exchange coupling in the synthetic antiferromagnet. Irrespective of the magnetic parameters and cell sizes, magnetization flop does not exist near zero applied field, indicating that magnetization flop is driven by the Zeeman energy.

• 응용통계연구
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• 제26권6호
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• pp.977-985
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• 2013

현실세계에는 두 가지 범주 이상으로 분류되는 경우가 많이 존재한다. 본 논문은 분류범주가 세 종류인 분류모형을 시각적으로 표현하는 방법인 ROC 곡면과 이 곡면 아래의 체적을 나타내는 VUS 통계량을 고려한다. 바젤 II에 기반한 부도확률에 관한 AUC 통계량의 판단기준을 ROC 곡면에서의 VUS에 대하여 확장하여, VUS에 의한 판별력 판단기준 13단계를 제안한다. 제안한 판단기준 각 단계에서의 VUS값에 대응하는 AUC, K-S 통계량 그리고 세 분포의 평균차이에 대한 범위를 탐색하고, 이들의 관계를 살펴봄으로써 VUS 통계량의 판별력 판단기준을 설정한다.

• ETRI Journal
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• 제41권6호
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• pp.850-862
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• 2019

This work investigated three-dimensional (3D) focused microwave thermotherapy (FMT) at 925 MHz for a human tissue mimicking phantom using the time reversal (TR) principle for musculoskeletal disorders. We verified the proposed TR algorithm by evaluating the possibility of 3D beam focusing through simulations and experiments. The simulation, along with the electromagnetic and thermal analyses of the human tissue mimicking phantom model, was conducted by employing the Sim4Life commercial tool. Experimental validation was conducted on the developed FMT system using a fabricated human tissue mimicking phantom. A truncated threshold method was proposed to reduce the unwanted hot spots in a normal tissue region, wherein a beam was appropriately focused on a target position. The validation results of the simulation and experiments obtained by utilizing the proposed TR algorithm were shown to be acceptable. Effective beam focusing at the desired position of the phantom could be achieved.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2004년도 ICEIC The International Conference on Electronics Informations and Communications
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• pp.143-146
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• 2004

Differentiated services (DiffServ) has been widely accepted as the service model to adopt for providing quality-of­service (QoS) over the next-generation IP networks. There is a growing need to support QoS in mobile ad hoc networks. Supporting DiffServ in mobile ad hoc networks, however, is very difficult because of the dynamic nature of mobile ad hoc networks, which causes network congestion. The network congestion induces long transfer packet delay and low throughput which make it very difficult to support QoS in mobile ad hoc networks. We propose DiffServ module to support differentiated service in mobile ad hoc networks through congestion control. Our DiffServ module uses the periodical rate control for real time traffic and also uses the best effort bandwidth concession when network congestion occurs. Network congestion is detected by measuring the packet transfer delay or bandwidth threshold of real time traffic. We evaluate our mechanism via a simulation study. Simulation results show our mechanism may offer a low and stable delay and a stable throughput for real time traffic in mobile ad hoc networks.

• JSTS:Journal of Semiconductor Technology and Science
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• 제4권2호
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• pp.94-99
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• 2004

silicided 50-nm-gate-length n-type Schottky barrier metal-oxide-semiconductor field-effect-transistors (SB-MOSFETs) with 5 nm gate oxide thickness are manufactured. The saturation current is $120{\mu}A/{\mu}m$ and on/off-current ratio is higher than $10^5$ with low leakage current less than $10{\mu}A/{\mu}m$. Novel phenomena of this device are discussed. The increase of tunneling current with the increase of drain voltage is explained using drain induced Schottky barrier thickness thinning effect. The abnormal increase of drain current with the decrease of gate voltage is explained by hole carrier injection from drain into channel. The mechanism of threshold voltage increase in SB-MOSFETs is discussed. Based on the extracted model parameters, the performance of 10-nm-gate-length SB-MOSFETs is predicted. The results show that the subthreshold swing value can be lower than 60 mV/decade.

• 대한치과기공학회지
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• 제42권3호
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• pp.197-201
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• 2020

Purpose: This study aimed to assess the quality of dental prostheses printed by digital light-processing (DLP) technology. Methods: Ten experimental models were prepared. The ten specimens that were printed by DLP technology constituted the DLP group. The ten specimens that were produced in the same model by the casting method constituted the control group. The marginal gaps of the 20 specimens produced were measured. These gaps were measured by a silicon replica technique at two abutments of the specimen. Therefore, 20 marginal gaps were measured in each group. An independent sample t-test was performed to compare the marginal gaps measured in the two groups (α=0.05). Results: According to the results of the measurement, there was a significant difference between the mean marginal gap of the control group (78.8 ㎛) and that of the DLP group (91.5 ㎛), p<0.001. Conclusion: Although the mean marginal gaps of dental fixed prostheses produced by the DLP method was higher than the mean marginal gap of those produced by the casting method, it was considered to be within the clinical threshold value suggested by some previous studies.

• 대한치과보철학회지
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• 제38권6호
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• pp.765-781
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• 2000

The purpose of this study was to compare the screw loosening characteristics of three avail-able cementation type abutments: one-piece cementation type abutment; two-piece cementation type abutment using titanium abutment screw; two-piece cementation type abutment using gold abutment screw. Two implant supported three-unit superstructures were fabricated using a pair of 3 kinds of abutments for each experimental model. Cyclic loading was applied on the specimen, and made to stop when the superstructure showed movement over threshold range. The loaded cycle was counted until the machine stopped. Frequency analysis was done to measure the change of natural frequency before and after the application of cyclic load and to find the effect of screw loosening on the change of natural frequency. The specimen assembly was modeled to perform the finite element analysis to see the distribution of the stress induced by the application of preload over the screw joint and to compare the pattern of the distribution of stress induced by the external force with the change of the preload condition. The following results were obtained: 1. The failure loading cycle of two-piece cementation type abutment using gold screw was significantly greater than those of the other groups. 2. One-piece cementation type abutment applied to multi-unit restoration case did not show greater resistance to screw loosening compared to two-piece cementation type abutments. 3. Frequency analysis showed decrease in natural frequency when screw loosening occured.

• 한국전기전자재료학회논문지
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• 제29권12호
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• pp.750-758
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• 2016

For the channel doping of shallow junction and retrograde well formation in CMOS, indium can be implanted in silicon. The retrograde doping profiles can serve the needs of channel engineering in deep MOS devices for punch-through suppression and threshold voltage control. Indium is heavier element than B, $BF_2$ and Ga ions. It also has low coefficient of diffusion at high temperatures. Indium ions can be cause the erode of wafer surface during the implantation process due to sputtering. For the ultra shallow junction, indium ions can be implanted for p-doping in silicon. UT-MARLOWE and SRIM as Monte carlo ion-implant models have been developed for indium implantation into single crystal and amorphous silicon, respectively. An analytical tool was used to carry out for the annealing process from the extracted simulation data. For the 1D (one-dimensional) and 2D (two-dimensional) diffused profiles, the analytical model is also developed a simulation program with $C^{{+}{+}}$ code. It is very useful to simulate the indium profiles in implanted and annealed silicon autonomously. The fundamental ion-solid interactions and sputtering effects of ion implantation are discussed and explained using SRIM and T-dyn programs. The exact control of indium doping profiles can be suggested as a future technology for the extreme shallow junction in the fabrication process of integrated circuits.