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Study on durability of Pt supported on graphitized carbon under simulated start-up/shut-down conditions for polymer electrolyte membrane fuel cells

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Journal of Energy Chemistry 2018年第1期27卷 326-334页

作者： Won Suk jung Department of Chemical Engineering University of South CarolinaColumbiaSC 29208USA

The primary issue for the commercialization of proton exchange membrane fuel cell（PEMFC） is the carbon corrosion of support under start-up/shut-down conditions. In this study, we employ the nanostructured graphitized carbon induced by heat-treatment. The degree of graphitization starts to increase between 900 and 1300 ℃ as evidenced by the change of specific surface area, interlayer spacing, and ID/IG value. Pt nanoparticles are deposited on fresh carbon black（Pt/CB） and carbon heat-treated at 1700 ℃（Pt/HCB17） with similar particle size and distribution. Electrochemical characterization demonstrates that the Pt/HCB17 shows higher activity than the Pt/CB due to the inefficient microporous structure of amorphous carbon for the oxygen reduction reaction. An accelerating potential cycle between 1.0 and 1.5 V for the carbon corrosion is applied to examine durability at a single cell under the practical start-up/shutdown conditions. The Pt/HCB17 catalyst shows remarkable durability after 3000 potential cycles. The Pt/HCB17 catalyst exhibits a peak power density gain of 3%, while the Pt/CB catalyst shows 65% loss of the initial peak power density. As well, electrochemical surface area and mass activity of Pt/HCB17 catalyst are even more stable than those of the Pt/CB catalyst. Consequently, the high degree of graphitization is essential for the durability of fuel cells in practical start-up/shut-down conditions due to enhancing the strong interaction of Pt and π-bonds in graphitized carbon.

关键词： Polymer electrolyte membrane fuel ceils Membrane electrolyte assembly Carbon corrosion Start-up/shut-down Durability

Tolerating Permanent State Transition Faults in Asynchronous Sequential Machines

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Journal of Computer Science & Technology 2016年第5期31卷 1028-1037页

作者： jung-Min Yang School of Electronics Engineering Kyungpook National University Daegu 41566 Korea

Corrective control theory lays a novel foundation for the fault-tolerant control of asynchronous sequential machines. In this paper, we present a corrective control scheme for tolerating permanent state transition faults in the dynamics of asynchronous sequential machines. By a fault occurrence, the asynchronous machine may be stuck at a faulty state, not responding to the external input. We analyze the detectability of the considered faults and present the necessary and sufficient condition for the existence of a controller that overcomes any permanent transition faults. Fault tolerance is realized by using potential reachability and asynchronous mechanisms in the machine. A case study on an asynchronous counter is provided to illustrate the proposed fault detection and tolerance scheme.

关键词： asynchronous sequential machine corrective control permanent fault fault tolerance

Next High Performance and Low Power Flash Memory Package Structure

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Journal of Computer Science & Technology 2007年第4期22卷 515-520页

作者： jung-Hoon Lee ERI Control Instrumentation EngineeringGyeongSang National UniversityJinju660-701Korea

In general, NAND flash memory has advantages in low power consumption, storage capacity, and fast erase/write performance in contrast to NOR flash. But, main drawback of the NAND flash memory is the slow access time for random read operations. Therefore, we proposed the new NAND flash memory package for overcoming this major drawback. We present a high performance and low power NAND flash memory system with a dual cache memory. The proposed NAND flash package consists of two parts, i.e., an NAND flash memory module, and a dual cache module. The new NAND flash memory system can achieve dramatically higher performance and lower power consumption compared with any conventionM NAND-type flash memory module. Our results show that the proposed system can reduce about 78% of write operations into the flash memory cell and about 70% of read operations from the flash memory cell by using only additional 3KB cache space. This value represents high potential to achieve low power consumption and high performance gain.

关键词： flash memory NAND-type NOR-type memory localities buffer or cache memory

Plant-pollinator metanetworks in fragmented landscapes:a simulation study

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Ecological Processes 2023年第1期12卷 415-424页

作者： Ehsan Rahimi Chuleui jung Agricultural Science and Technology Institute Andong National UniversityAndong City 36729Republic of Korea Department of Plant Medicals Andong National UniversityAndong CityRepublic of Korea

Background The topology of the plant-pollinator network can be explained by the species’abundance and their random ***-pollinator networks can be studied in the context of a landscape,because each patch can accommodate a certain local *** populations of pollinators in the landscape can be connected through migration and then constitute a metanetwork that is known as a combination of spatial and ecological *** this regard,habitat fragmentation can affect the topology of plant-pollinator metanetworks through changes in the species abundance and limiting their ***,it is not clear what pattern(fragmented or aggregated)of the landscape structure can accommodate networks with a higher degree of *** we created simulated landscapes with different forest proportions scenarios(from 5%to 50%of the total landscape)and degrees of ***,for each landscape,we limited the proportion of pollinators to the forest *** assumed that plants and pollinators are randomly distributed around the landscape and interact *** used landscape metrics to measure different aspects of landscape structure and bipartite metrics for calculating the degree of specialization in plant-pollinator *** The statistical relationship between bipartite and landscape metrics showed that the relationship between the topology of plant-pollinator networks and the landscape structure is affected by the forest amount in the landscape and the degree of forest *** also found that according to the nestedness and H2(a measure of specialization)metrics,fragmented landscapes contain more general plant-pollinator *** Our findings suggest that fragmented landscapes,characterized by scattered forest patches,can promote higher levels of interaction between limited pollinators and diverse flowers,leading to more general plant-pollinator networks.

关键词： Plant–pollinator metanetwork Habitat fragmentation Simulated landscape Landscape metrics Bipartite metrics

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Asymptotic T_u-Toeplitzness of weighted composition operators on H^2

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Science China Mathematics 2018年第5期61卷 881-896页

作者： Sungeun jung Department of Mathematics Hankuk University of Foreign Studies

Given a unilateral forward shift S acting on a complex,separable,infinite dimensional Hilbert space H,an asymptotically S-Toeplitz operator is a bounded linear operator T on H satisfying that{S^(*n)T S^n}is convergent with respect to one of the topologies commonly used in the algebra of bounded linear operators on *** this paper,we study the asymptotic T_u-Toeplitzness of weighted composition operators on the Hardy space H^2,where u is a nonconstant inner function.

关键词： Toeplitz operator asymptotically S-Toeplitz operator weighted composition operator inner function

Calcium-and sulfate-functionalized artificial cathode–electrolyte interphases of Ni-rich cathode materials

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Rare Metals 2021年第10期40卷 2793-2801页

作者： Kwangeun jung Taeeun Yim Department of Chemistry Incheon National UniversityIncheon 22012Republic of Korea

Ni-rich lithium nickel–cobalt-manganese oxides(NCM) are considered the most promising cathode materials for lithium-ion batteries(LIBs);however, relatively poor cycling performance is a bottleneck preventing their widespread use in energy systems. In this work, we propose the use of a dually functionalized surface modifier, calcium sulfate(CaSO_(4), CSO), in an efficient one step method to increase the cycling performance of Ni-rich NCM cathode materials. Thermal treatment of LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811) cathode materials with a CSO precursor allows the formation of an artificial Ca-and SO_(x)-functionalized cathode–electrolyte interphase(CEI) layer on the surface of Ni-rich NCM cathode materials. The CEI layer then inhibits electrolyte decomposition at the interface between the Ni-rich NCM cathode and the electrolyte. Successful formation of the CSO-modified CEI layer is confirmed by scanning electron microscopy(SEM) and Fourier transform infrared(FTIR) spectroscopy analyses, and the process does not affect the bulk structure of the Ni-rich NCM cathode material. During cycling, the CSO-modified CEI layer remarkably decreases electrolyte decomposition upon cycling at both room temperature and 45 ℃, leading to a substantial increase in cycling retention of the cells. A cell cycled with a 0.1 CSO-modified(modified with 0.1% CSO)NCM811 cathode exhibits a specific capacity retention of90.0%, while the cell cycled with non-modified NCM811 cathode suffers from continuous fading of cycling retention(74.0%) after 100 cycles. SEM, electrochemical impedance spectroscopy(EIS), X-ray photoelectron spectroscopy(XPS), and inductively coupled plasma mass spectrometry(ICP-MS) results of the recovered electrodes demonstrate that undesired surface reactions such as electrolyte decomposition and metal dissolution are well controlled in the cell because of the artificial CSO-modified CEI layer present on the surface of Ni-rich NCM811 cathodes.

关键词： Lithium-ion battery Cathode Cathode–electrolyte interphase Calcium sulfate Electrochemical performance

A Miniaturized Crawler Design Based on an Origami-inspired and Geometrically Constrained Spherical Six-bar Linkage

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Journal of Bionic Engineering 2024年第1期21卷 166-176页

作者： Subin Chae Gwang-Pil jung Department of Mechanical and Automotive Engineering Seoul National University of Science and TechnologySeoul 01811South Korea

This paper focuses on a newly developed transmission for a milli-scale eight-legged crawling robot called *** transmission allows intuitive steering by directly changing the direction of the propulsion *** transmission is based on the constrained spherical six-bar *** constrained spherical six-bar linkage passes only reciprocating motion out of the motor’s rotating motion,allowing the crawling legs to kick the ground and obtain *** is achieved by adjusting the geometric constraints of the spherical six-bar using a servomotor,allowing the direction of propulsion to be *** a result,the OriSCO can move along the ground at a speed of 2.15 body lengths/s,and the robot is 60 mm long.

关键词： Bio-inspired robot Crawler:Crawling robot Direction change Spherical six-bar linkage

Effects of annealing temperature and neodymium concentration on structural and photoluminescence properties of Nd^(3+)-doped Y_(2)O_(3)-SiO_(2) powders

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Journal of Rare Earths 2021年第6期39卷 651-656,I0002页

作者： NoSoung Myoung Gyeong Bok jung Advanced Photonics Research Institute Gwangju Institute of Science and TechnologyGwangju 61005South Korea Department of Physics Education Chosun UniversityGwangju 61452South Korea

We report the structural and photoluminescence(PL) properties of Nd^(3+)-doped Y_(2)O_(3)-SiO_(2) powders(Y_(2)O_(3)-SiO_(2):Nd^(3+)) as functions of annealing temperature and Nd^(3+) ion doping concentration.Y_(2)O_(3)-SiO_(2):Nd^(3+)powders were prepared using the high-energy ball-milling(HEBM) method,and their structural and PL properties were investigated using X-ray diffraction(XRD),Fourier transform infrared(FTIR) spectroscopy,and PL *** XRD results reveal a cubic phase without impurities,and the peak broadening decreases with an increase in annealing temperature due to the increase in the crystallite *** PL emission intensity increases with an increase in annealing *** highest PL emission intensity is observed for the 300-min milled mixture annealed at 1000℃ for 1 h with a Nd^(3+) concentration of 1 mol%.The PL peaks excited by 800 nm radiation were detected,centered at 1080 nm(^(4)F_(3/2)→^(4)I_(11/2)) and 1350 nm(^(4)F_(3/2)→^(4)I_(13/2)).

关键词： Nd^(3+)-doped Y_(2)O_(3)-SiO_(2)powders High-energy ball-milling method Near infrared photoluminescence emission Rare earth Annealing temperature

Lattice Preferred Orientation, Water Content, and Seismic Anisotropy of Orthopyroxene

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Journal of Earth Science 2010年第5期21卷 555-568页

作者： Haemyeong jung Munjae Park Sejin jung Jaeseok Lee Tectonophysics Laboratory School of Earth and Environmental Sciences Seoul National University Seoul 151-747 Korea

Lattice preferred orientation （LPO） and seismic anisotropy of orthopyroxene （enstatite） in mantle xenoliths from Spitsbergen, Svalbard, near the Arctic, are studied. LPOs of enstatite were determined using electron backseattered diffraction （EBSD）. We found four types of LPOs of orthopyroxene and defined them as type-AC, -AB, -BC, and -ABC. Type-AC LPO of orthopyroxene is defined as （100） plane aligned subparallel to foliation and [001] axis aligned subparallel to lineation. Type-AB LPO is defined as （100） plane aligned subparallel to foliation and [010] axis aligned subparallel to linea- tion. Type-BC LPO is defined as （010） plane aligned subparallel to foliation and [001] axis aligned subparallel to lineation. Type-ABC LPO is defined as both （100） and （010） planes aligned subparallel to foliation with a girdle distribution of both [100] and [010] axes normal to lineation and [001] axis aligned subparallel to lineation. We report for the first time the type-AB, -BC, and -ABC LPO of orthopyroxerie. We found that the LPO pattern has a correlation with the content of orthopyroxene in the specimen. Nicolet 6700 FTIR （Fourier transformation infrared） study of enstatite showed that type-AC LPO was observed mostly in the samples of enstatite with low water content. It is found that the strength of the LPO of enstatite decreases with increasing water content and has a correlation with the strength of the LPO of olivine： the stronger the LPO of enstatite, the stronger the LPO of olivine. Seismic anisotropy of enstatite was smaller than that of olivine in the same specimen.

关键词： orthopyroxene lattice preferred orientation seismic anisotropy mantle xenolith Spitsbergen FTIR.