• Nuclear Engineering and Technology
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• 제29권6호
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• pp.459-467
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• 1997

The steady-state behavior of recycling neutral atoms in a tokamak edge region has been analyzed through a two-dimensional Monte Carlo simulation. A particle tracking algorithm used in earlier research on the neutral particle transport is applied to this Monte Carlo simulation in order to perform more accurate calculations with the EDGETRAN code which was previously developed for a two-dimensional edge plasma transport in the authors' laboratory. The physical model of neutral recycling includes charge-exchange and ionization interactions between plasmas and neutral atoms. The reflection processes of incident particles on the device wall are described by empirical formulas. Calculations for density, energy, and velocity distributions of neutral deuterium-tritium atoms have been carried out for a medium-sized tokamak with a double-null configuration based on the KT-2 conceptual design. The input plasma parameters such as plasma density, ion and electron temperatures, and ion fluid velocity are provided from the EDGETRAN calculations. As a result of the present numerical analysis, it is noticed that a significant drop of the neutral atom density appears in the region of high plasma density and that the similar distribution of neutral energy to that of plasma ions is present as frequently reported in other studies. Relations between edge plasma conditions and the neutral recycling behavior are discussed from the numerical results obtained herein.

• Journal of the Korean Electrochemical Society
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• 제22권4호
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• pp.172-176
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• 2019

The first commercialized cathode material, $LiCoO_2$, suffers from disadvantages such as high cost and toxicity and also possesses safety problems. The nickel-rich $LiNi_{0.9}Mn_{0.1}O_2$ cathode material, used as an alternative to $LiCoO_2$, has highly reversible capacity and high energy density. So, the nickel-rich $LiNi_{0.9}Mn_{0.1}O_2$ cathode material is widely used as an alternative to $LiCoO_2$ due to its highly reversible capacity and high energy density. However, $LiNi_{0.9}Mn_{0.1}O_2$ has several disadvantages as well, such as poor cycle performance and poor thermal instability. To address these problems, we synthesized a new material, $LiNi_{0.5}Mn_{0.5}O_2$, as a shell on the surface of a core to suppress the surface degradation. The new material showed high structural and thermal stabilities and could also maintain a high capacity. The capacity retention of the core-shell cathode (87.7%) was better than that of the core cathode (76.9%) after 50 cycles. Analysis using differential scanning calorimetry revealed that the heat generation in the core-shell cathode ($65.9Jg^{-1}$) was lower than that in the core cathode ($559.7Jg^{-1}$).

• Transactions of the Korean hydrogen and new energy society
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• 제30권4호
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• pp.303-311
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• 2019

Reversible solid oxide fuel cell (RSOFC) has become a prospective device for energy storage and hydrogen production. Many studies have been conducted around the world focusing on system efficiency improvement and realization. The system should have not only high efficiency but also a certain level of simplicity for stable operation. External waste steam utilization was proved to remarkably increase the efficiency at solid oxide electrolysis system. In this study, RSOFC system coupled with waste steam was proposed and optimized in term of simplicity and efficiency. Ejector for fuel recirculation is selected due to its simple design and high stability. Three system configurations using ejector for fuel recirculation were investigated for performance of design condition. In parametric study, the system efficiencies at different current density were analyzed. The system configurations were simulated using validated lumped model in EBSILON(R) program. The system components, balance of plants, were designed to work in both electrolysis and fuel cell modes, and their off-design characteristics were taken into account. The base case calculation shows that, the system with suction pump results in slightly lower efficiency but stack can be operated more stable with same inlet pressure of fuel and air electrode.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 한국전기전자재료학회 2002년도 춘계학술대회 논문집 초전도 자성체
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• pp.88-95
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• 2002

Recent development in the field of RE-Ba-Cu-O (REBCO, RE: Y or rare earth elements) bulk high-Tc superconductors (HTS) is reviewed in the present paper. After the fatal weak link problem of sintered REBCO superconductors has been overcome by melt processing, this field has been greatly advanced during last ten years. The critical current density $J_c$ at 77 K has been enhanced by introducing effective flux pinning sites into the $REBa_2Cu_3O_y$ (RE123) superconducting matrix. Large melt-textured REBCO bulk crystals have been fabricated with the TSMG(top-seeded melt growth) technique. Mechanical properties of REBCO bulks have been improved by using the Ag additive or epoxy resin. Real bulk applications such as current lead, fault current limiter, flywheel energy storage system, magnetic field source, magnetic separation system, and etc., surely come true near future.

• Journal of Electrochemical Science and Technology
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• 제15권1호
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• pp.14-31
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• 2024

The text highlights the growing need for eco-friendly energy storage and the potential of metal-organic frameworks (MOFs) to address this demand. Despite their promise, challenges in MOF-based energy storage include stability, reproducible synthesis, cost-effectiveness, and scalability. Recent progress in supercapacitor materials, particularly over the last decade, has aimed to overcome these challenges. The review focuses on the morphological characteristics and synthesis methods of MOFs used in supercapacitors to achieve improved electrochemical performance. Various types of MOFs, including monometallic, binary, and tri-metallic compositions, as well as derivatives like hybrid nanostructures, sulfides, phosphides, and carbon composites, are explored for their energy storage potential. The review emphasizes the quest for superior electrochemical performance and stability with MOF-based materials. By analyzing recent research, the review underscores the potential of MOF-based supercapacitors to meet the increasing demands for high power and energy density solutions in the field of energy storage.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제18권5호
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• pp.1390-1411
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• 2024

Underwater Wireless Sensors Networks (UWSNs) are deployed in remotely monitored environment such as water level monitoring, ocean current identification, oil detection, habitat monitoring and numerous military applications. Providing scalable and efficient routing is very challenging in UWSNs due to the harsh underwater environment. The biggest difficulties are the nodes inherent movement due to water current, long delay in data transmission, low bandwidth of the acoustic signal, high error rate and energy scarcity in battery powered nodes. Many routing protocols have been proposed to solve the aforementioned problems. There are three broad categories of routing protocols namely depth based, energy based and vector-based routing. Vector Based Forwarding protocols perform routing through virtual pipeline by defining their radius which give proper direction to packets communication. We proposed a routing protocol termed as Path-Oriented Energy Scaled Expanded Vector Based Forwarding (PESEVBF). PESEVBF takes into account all parameters; holding time, the source nodes packets routing path and void holes creation on the second hop; PESEVBF not only considers the packet upward advancement but also focus on density of the forwarded nodes in terms of number of potential forwarding and suppressed nodes for path selection. Node selection in resultant holding time is based on minimum Path Factor (PF) value. Moreover, the suppressed node will be selected for packet forwarding to avoid the void holes occurrences on the second hop. Performance of PESEVBF is compared with other routing protocols using matrices such as energy consumption, packet delivery ratio, packets dropping ratio and duplicate packets creation indicating considerable performance improvement.

• Transactions of the Korean hydrogen and new energy society
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• 제27권5호
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• pp.526-532
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• 2016

In this study, we synthesized a mediator immobilized biocatalyst([FCA/GOx]/PEI/CNT) by surface modification using ferrocene carboxylic acid(FCA), and evaluated its performance as anode catalyst for biofuel cell. Through the application of FCA on glucose oxidase (GOx), the free amine groups on the lysine residue of GOx surface reacted with carboxylic acid of FCA and make amide bond between GOx and FCA. As the result of that, the electron transfer of catalyst was increased up to 1.91 times($0.468mA{\cdot}cm^{-2}$) than the catalyst without surface modification (GOx/PEI/CNT), and high maxium power density of $1.79mA{\cdot}cm^{-2}$ was gained.

• Nuclear Engineering and Technology
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• 제45권7호
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• pp.979-986
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• 2013

Uranium metal particle dispersion plates have been proposed as targets for Molybdenum-99 (Mo-99) production to improve the radioisotope production efficiency of conventional low enriched uranium targets. In this study, uranium powder was produced by centrifugal atomization, and miniature target plates containing uranium particles in an aluminum matrix with uranium densities up to 9 $g-U/cm^3$ were fabricated. Additional heat treatment was applied to convert the uranium particles into UAlx compounds by a chemical reaction of the uranium particles and aluminum matrix. Thus, these target plates can be treated with the same alkaline dissolution process that is used for conventional $UAl_x$ dispersion targets, while increasing the uranium density in the target plates.

• Transactions of the Korean hydrogen and new energy society
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• 제26권3호
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• pp.234-240
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• 2015

In the face of the world's growing energy storage needs, liquid hydrogen offers a high energy density solution for the storage and transport of energy throughout society. A 5 L liquid hydrogen storage tank has been designed, fabricated and tested to investigate boil-off rate of liquid hydrogen. As the insulation plays a key role on the cryogenic vessels, various insulation methods have been employed. To reduce heat conduction loss, the epoxy resin-based insulation supports G-10 were used. To minimize radiation heat loss, vapor cooled radiation shield, multi-layer insulation, and high vacuum were adopted. Mass flow meter was used to measure boil-off rate of the 5 L cryogenic vessel. A series of performance tests were done for liquid nitrogen and liquid hydrogen to compare with design parameters, resulting in the boil-off rate of 1.7%/day for liquid nitrogen and 16.8%/day for liquid hydrogen at maximum.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 추계학술대회 논문집
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• pp.171-171
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• 2009

The electrodes are usually made of a porous mixture of carbon-supported platinum and ionomers. $SnO_2$ particles provide as supports that have been used for DMFCs, and it have high catalytic activities toward methanol oxidation. The main advantage of $SnO_2$ supported electrodes is that it has strong chemical interactions with metallic components. The high activity to a synergistic bifunctional mechanism in which Pt provides the adsorption sites for CO, while oxygen adsorbs dissociative on $SnO_2$. The reaction between the adsorbed species occurs at the Pt/$SnO_2$ boundary. The morphological observations were characterized by FESEM and transmission electron microscopy (TEM). $SnO_2$ particles crystallinity was analyzed by the X-ray diffraction (XRD). The surface bonded state of the $SnO_2$ particles and electrode materials were observed by the X-ray photoelectron spectroscopy (XPS). The electric properties of the Pt/$SnO_2$ catalyst for methanol oxidation have been investigated by the cyclic voltametry (CV) in 0.1M $H_2SO_4$ and 0.1M MeOH aqueous solution. The peak current density of methanol oxidation was increased as the $SnO_2$ content in the anode catalysts increased. Pt/$SnO_2$ catalysts improve the removal of CO ads species formed on the platinum surface during methanol electro-oxidation.