• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.5
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• pp.682-687
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• 2022

In this paper, the research results on monolithic three-dimensional integrated-circuit (M3DICs) stacked with tunneling field effect transistors (TFETs) are introduced. Unlike metal-oxide-semiconductor field-effect transistors (MOSFETs), TFETs are designed differently from the layout of symmetrical MOSFETs because the source and drain of TFET are asymmetrical. Various monolithic 3D inverter (M3D-INV) structures and layouts are possible due to the asymmetric structure, and among them, a simple inverter structure with the minimum metal layer is proposed. Using the proposed M3D-INV, this M3D logic gates such as NAND and NOR gates by sequentially stacking TFETs are proposed, respectively. The simulation results of voltage transfer characteristics of the proposed M3D logic gates are investigated using mixed-mode simulator of technology computer aided design (TCAD), and the operation of each logic circuit is verified. The cell area for each M3D logic gate is reduced by about 50% compared to one for the two-dimensional planar logic gates.

• Nuclear Engineering and Technology
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• v.53 no.5
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• pp.1676-1685
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• 2021

We develop a new high-fidelity multiphysics model to simulate boron chemistry in the porous Chalk River Unidentified Deposit (CRUD) deposits. Heat transfer, capillary flow, solute transport, and chemical reactions are fully coupled. The evaporation of coolant in the deposits is included in governing equations modified by the volume-averaged assumption of wick boiling. The axial offset anomaly (AOA) of the Seabrook nuclear power plant is simulated. The new model reasonably predicts the distributions of temperature, pressure, velocity, volumetric boiling heat density, and chemical concentrations. In the thicker CRUD regions, 60% of the total heat is removed by evaporative heat transfer, causing boron species accumulation. The new model successfully shows the quantitative effect of coolant evaporation on the local distributions of boron. The total amount of boron in the CRUD layer increases by a factor of 1.21 when an evaporation-driven increase of soluble and precipitated boron concentrations is reflected. In addition, the concentrations of B(OH)₃ and LiBO₂ are estimated according to various conditions such as different CRUD thickness and porosity. At the end of the cycle in the AOA case, the total mass of boron incorporated in CRUD deposits of a reference single fuel rod is estimated to be about 0.5 mg.

• Journal of the Korean Geotechnical Society
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• v.25 no.9
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• pp.5-17
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• 2009

The microcomputer program PileNSF (Pile Negative Skin Friction) is developed by the authors in a graphical user interface (GUI) environment using $MATLAB^{(R)}$ for predicting the bearing capacity of a pile embedded in a consolidating ground by surcharge loading. The proposed method extends the one-dimensional soil-pile model based on the nonlinear load transfer method in OpenSees to perform an advanced one-dimensional consolidation settlement analysis based on finite strain. The developed program has significant features of incorporating Mikasa's finite strain consolidation theory that accounts for reduction in the thickness of the clay layer as well as the change of the soil-pile interface length during the progress of consolidation. In addition, the consolidating situation of the ground by surcharge filling after the time of pile installation can also be considered in the analysis. The program analysis by the presented method has been verified and validated with several case studies of long-term test on single piles subjected to negative skin friction. Predicted results of negative skin friction (downdrag and dragload) as a result of long from consolidation settlement are shown to be in good agreement with measured and observed case data.

• Journal of the Korean Geotechnical Society
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• v.22 no.11
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• pp.113-122
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• 2006

Although a number of static pile load tests have been performed in this country, re-consideration on the interpretation and loading method is needed, because of their less usefulness in practice. For this study, a static loading testing was performed for a long instrumented PHC pile, which was installed in sand layer overlying thick soft clay. The shaft resistance of the pile had been monitored for a long time after installation, and then the static load testing was performed by the quick load test, unlike the recent Korean practice. Using the measured data, the elastic modulus of pile, residual stress and true resistance on the pile were determined. In the event, it was found that the residual stress on the pile, which remained prior to the static loading, significantly affects the shaft and toe resistances. Also, it was realized that the setup effect for the long pile is significant.

• Transactions of the Korean hydrogen and new energy society
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• v.34 no.2
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• pp.178-186
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• 2023

Three activation methods (constant voltage, current cycling, and hydrogen pumping) were applied to investigate the effects on the performance of the membrane electrode assembly (MEA) loaded with PtCo/C catalyst. The current cycling protocol took the shortest time to activate the MEA, while the performance after activation was the worst among the all activation methods. The constant voltage method took a moderate activation time and exhibited the best performance after activation. The hydrogen pumping protocol took the longest time to activate the MEA with moderate performance after activation. According to the distribution of relaxation time analysis, the improved performance after the activation mainly comes from the decrease of charge transfer resistance rather than the ionic resistance in the cathode catalyst layer, which suggests that the existence of water on the electrode is the key factor for activation.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.6
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• pp.53-62
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• 2018

Follofwing the accelerating speed-up of trains and rising demand for large-volume transfer capacity, not only in Korea, but also around the world, track structures for trains have been improving consistently. Precast concrete slab track (PST), a concrete structure track, was developed as a system that can fulfil new safety and economic requirements for railroad traffic. The purpose of this study is to provide the information required for the development and design of the system in the future, by analyzing the behavior of each structural member of the PST system. The stress distribution result for different combinations of appropriate loads according to the KRL-2012 train load and KRC code was analyzed by conducting a three-dimensional finite element analysis, while the result for different thicknesses of the grouting layer is also presented. Among the structural members, the largest stress took place on the grouting layer. The stress changed sensitively following the thickness and the combination of loads. When compared with a case of applying only a vertical KRL-2012 load, the stress increased by 3.3 times and 14.1 times on a concrete panel and HSB, respectively, from the starting load and temperature load. When the thickness of the grouting layer increased from 20 mm to 80 mm, the stress generated on the concrete panel decreased by 4%, while the stress increased by 24% on the grouting layer. As for the cracking condition, tension cracking was caused locally on the grouting layer. Such a result indicates that more attention should be paid to the flexure and tension behavior from horizontal loads rather than from vertical loads when developing PST systems. In addition, the safety of each structural member must be ensured by maintaining the thickness of the grouting layer at 40 mm or more.

• Bulletin of the Korean Chemical Society
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• v.33 no.5
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• pp.1627-1637
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• 2012

The coupling reaction between 5-bromo-3-phenylbenzo[c]isoxazole and diphenylamine followed by further condensation with a mono-, di- or ter-acetyl aromatic compound in the presence of diphenyl phosphate at $145^{\circ}C$ gave a novel asymmetric diarylquinolines, oligoquinolines with diphenylamine endgroups, and a first generation quinoline dendrimer in 41-82% isolated yield. The electrochemical and photophysical properties of the oligoquinolines were characterized by cyclic voltammograms (CVs) and spectroscopy. All the quinolines emit bright sky blue light due to charge transfer from quinoline group to diphenly amine with very high quantum efficiency (> 90%). Organic light-emitting diodes (OLEDs) were fabricated using these quinolines as emitting materials. Among different device architectures explored, OLEDs with a structure of ITO/PEDOT (40 nm)/TAPC (15 nm)/D-A quinoline (40 nm)/TPBI (30 nm)/LiF (1 nm)/Al using TAPC as an electron blocking layer and TPBI as a hole blocking layer gave the best performance. A high external quantum efficiency in the range of 1.2-2.3% were achieved in all the quinolines with the best performance in BBQA(5). Our results indicate diarylamino-substituted oligoquinoline and dendrimer are promising materials for OLEDs applications.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.224-224
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• 2012

For decades, carbon fiber has expanded their application fields from reinforced composites to energy storage and transfer technologies such as electrodes for super-capacitors and lithium ion batteries and gas diffusion layers for proton exchange membrane fuel cell. Especially in fuel cell, water repellency of gas diffusion layer has become very important property for preventing flooding which is induced by condensed water could damage the fuel cell performance. In this work, we fabricated superhydrophobic network of carbon fiber with high aspect ratio hair-like nanostructure by preferential oxygen plasma etching. Superhydrophobic carbon fiber surfaces were achieved by hydrophobic material coating with a siloxane-based hydrocarbon film, which increased the water contact angle from $147^{\circ}$ to $163^{\circ}$ and decreased the contact angle hysteresis from $71^{\circ}$ to below $5^{\circ}$, sufficient to cause droplet roll-off from the surface in millimeter scale water droplet deposition test. Also, we have explored that the condensation behavior (nucleation and growth) of water droplet on the superhydrophobic carbon fiber were significantly retarded due to the high-aspect-ratio nanostructures under super-saturated vapor conditions. It is implied that superhydrophobic carbon fiber can provide a passage for vapor or gas flow in wet environments such as a gas diffusion layer requiring the effective water removal in the operation of proton exchange membrane fuel cell. Moreover, such nanostructuring of carbon-based materials can be extended to carbon fiber, carbon black or carbon films for applications as a cathode in lithium batteries or carbon fiber composites.

• Journal of the Korean Geotechnical Society
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• v.32 no.7
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• pp.35-45
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• 2016

Estimation of vertical bearing capacity is critical in the design of bucket foundation used to support offshore structure. Empirical formula and closed form solutions for bucket foundations in uniform sand or clay profiles have been extensively studied. However, the vertical bearing capacity of bucket foundations in alternating layers of sand overlying clay is not well defined. We performed a series of two-dimensional axisymmetric finite element analyses on bucket foundations in sand overlying clay soil, using elasto-plastic soil model. The load transfer mechanism is investigated for various conditions. Performing the parametric study for the friction angles, undrained shear strengths, thickness of sand layer, and aspect ratios of foundation, we present the predictive charts for determining the vertical bearing capacities of bucket foundations in sand overlying clay layer. In addition, after comparing with the finite element analysis results, it is found that linear interpolation between the design charts give acceptable values in these ranges of parameters.

• Tribology and Lubricants
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• v.27 no.4
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• pp.193-197
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• 2011

Friction behavior of nanoporous anodic aluminum oxide(AAO) film was investigated. A 60 ${\mu}m$ thick AAO film having nanopores of 45 nm diameter with 105 nm interpore-diatance was fabricated by mild anodization process. The AAO film was then saturated with paraffinic oil. Reciprocating ball-on-flat sliding friction tests using 1 mm diameter steel ball as the counterpart were carried out with normal load ranging from 0.1 N to 1 N in an ambient environment. The morphology of worn surfaces were analyzed using scanning electron microscopy. The friction coefficient significantly increased with the increase of load. The boundary lubrication layer of paraffinic oil contributed to the lower friction at relatively low load (0.1 N), but it is less effective at high load (1 N). Plastic deformed layer patches were formed on the worn surface of oil-enriched AAO at relatively low load (0.1 N) without evidence of tribochemical reaction. On the other hand, thick tribolayers were formed on the worn surface of both oil-enriched and as-prepared AAO at relatively high load (1 N) due to tribochemical reaction and material transfer.