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Recent advances in nanomaterials for high-performance Li–S batteries

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Journal of Energy Chemistry 2020年第8期29卷 86-106,I0004页

作者： James E.Knoop Seongki ahn Joint School of Nanoscience and Nanoengineering North Carolina Agricultural and Technical State UniversityGreensboroNC 27401USA Research Organization for Nano and Life Innovation Waseda University513WasedatsurumakichoShinjuku-kuTokyo 162-0041Japan

This article reviews nanotechnology as a practical solution for improving lithium-sulfur batteries. Lithiumsulfur batteries have been widely examined because sulfur has many advantageous properties such as a high crustal abundance, low environmental impact, low cost, high gravimetric(2600 W h kg-1) and volumetric(2800 W h L-1) energy densities, assuming complete conversion of sulfur to lithium sulfide(Li2S)upon lithiation. However, lithium-sulfur batteries have not yet reach commercialization due to demerits involving the formation of soluble lithium polysulfides(Li2Sn, n=3–8), low electrical conductivity, and low loading density of sulfur. These issues arise mainly due to the polysulfide shuttle phenomenon and the inherent insulating nature of sulfur. To overcome these issues, strategies have been pursued using nanotechnology applied to porous carbon nanocomposites, hollow one-dimensional carbon nanomaterials, graphene nanocomposites, and three-dimensional carbon nanostructured matrices. This paper aims to review various solutions pertaining to the role of nanotechnology in synthesizing nanoscale and nanostructured materials for advanced and high-performance lithium–sulfur batteries. Furthermore, we highlight perspective research directions for commercialization of lithium–sulfur batteries as a major power source for electric vehicles and large-scale electric energy storage.

关键词： Nanotechnology Lithium–sulfur batteries Carbon nanomaterials Nanocomposite sulfur 3D nanostructured materials

Generalized passivity-based chaos synchronization

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Applied Mathematics and Mechanics(English Edition) 2010年第8期31卷 1009-1018页

作者： C.K.ahn Faculty of the Division of Electronics and Control Engineering Wonkwang University

In this paper, a new passivity-based synchronization method for a general class of chaotic systems is proposed. Based on the Lyapunov theory and the linear matrix inequality （LMI） approach, the passivity-based controller is presented to make the synchronization error system not only passive but also asymptotically stable. The proposed controller can be obtained by solving a convex optimization problem represented by the LMI. Simulation studies for the Genesio-Tesi chaotic system and the Qi chaotic system are presented to demonstrate the effectiveness of the proposed scheme.

关键词： passivity-based synchronization linear matrix inequality (LMI) chaotic systems Lyapunov theory

H∞ stability conditions for delayed neural networks with external disturbances and norm-bounded uncertainties:Delay independent and dependent criteria

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Science China(Information Sciences) 2011年第8期54卷 1691-1701页

作者： Choon Ki ahn Department of Automotive Engineering Seoul National University of Science & Technology

In this paper,we propose new delay independent and dependent H ∞ stability conditions for delayed neural networks with external disturbances and norm-bounded *** conditions are presented to not only guarantee the asymptotical stability but also reduce the effect of external disturbance to an Hnorm constraint. The proposed conditions are represented by linear matrix inequalities （LMIs）.Optimal Hnorm bounds are obtained easily by solving convex problems in terms of *** applicability of these conditions is illustrated by numerical examples.

关键词： H_∞ analysis delayed neural networks uncertainty disturbance linear matrix inequality (LMI)

Influence of cutting parameters on surface characteristics of cut section in cutting of Inconel 718 sheet using CW Nd:YAG laser

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中国有色金属学会会刊：英文版 2009年第B09期19卷 32-39页

作者： Dong-Gyu ahn Kyung-Won BYUN Department of Mechanical Engineering Chosun University

Recently, laser cutting technologies begin to use for manufacturing mechanical parts of Inconel super-alloy sheet due to difficulties of machining of the Inconel material as a results of its extremely tough nature. The objective of this work is to investigate the influence of cutting parameters on surface characteristics of the cut section in the cutting of Inconel 718 super-alloy sheet using CW Nd:YAG laser through laser cutting experiments. Normal cutting experiments were performed using a laser cutting system with six-axis controlled automatic robot and auto-tracking system of the focal distance. From the results of the experiments, the effects of the cutting parameters on the surface roughness, the striation formation and the microstructure of the cut section were examined. In addition, an optimal cutting condition, at which the surface roughness is minimized and both the delayed cutting phenomenon and the micro-cracking are not initiated, is estimated to improve both the part quality and the cutting efficiency.

关键词：激光切割技术 Inconel YAG激光器表面特性 Nd 表面粗糙度分切自动跟踪系统

Efficient construction of provably secure steganography under ordinary covert channels

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Science China(Information Sciences) 2012年第7期55卷 1639-1649页

作者： ahn Gail-Joon School of Computing Informaticsand Decision Systems EngineeringArizona State University

Steganography is the science of hiding information within seemingly harmless messages or innocent *** paper addresses the problems of efficient construction of secure steganography in ordinary covert *** relying on any sampling assumption,we provide a general construction of secure steganography under computational *** results show that unpredictability of mapping function in covertext sampler is indispensable for secure stegosystem on indistinguishability against adaptive chosen hiddentext *** completely prove that computationally secure steganography can be constructed on pseudorandom function and unbiased sampling function under ordinary covert channels,that is,its security is inversely proportional to the sum of errors of these two functions,as well as the legth of *** importantly,our research is not dependent upon pseudorandom ciphertext assumption of cryptosystem or perfect sampling ***,our results are practically useful for construction and analysis of secure stegosystems.

关键词： steganography cryptography indistinguishability sampler unpredictability adversary models

Effect of Ni and Mn on the Mechanical Properties of 22Cr Microduplex Stainless Steel

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Acta Metallurgica Sinica(English Letters) 2015年第1期28卷 32-38页

作者： Jun-Young Park Yong-Sik ahn Department of Materials Science and Engineering Pukyong National University

The tensile properties of 22Cr–2Ni–4Mn–0.2N micro-duplex stainless steels with different Ni and Mn contents were investigated. Duplex stainless steels were vacuum induction melted and hot rolled, then annealed at 1,000–1,100 °C, at which temperature both the austenite and ferrite phases were stable. The volume fraction of the ferrite phase was markedly affected by the alloying elements of Mn and Ni; 1 wt% of Mn was equivalent to 0.4 wt% of Ni. All of the steels tested at room temperature showed the common strain-hardening behavior, while the steels tested at lower temperatures（-30 or-50 °C）showed a distinct inflection point in their stress–strain curves, which resulted from the transformation of the austenite to straininduced martensite. The onset strain（e0） of the inflection point in the stress–strain curve depended on the Md30 value of the steel. Testing at lower temperatures resulted in smaller e0 and consequently higher strengths and fracture strains（ef）. The tensile behavior was examined from the perspective of austenite stability of the micro-duplex stainless steels with the different Ni and Mn contents.

关键词： Duplex stainless steel Microstructure Mechanical property Alloy composition

Influence of process parameters on drilling characteristics of Al 1050 sheet with thickness of 0.2 mm using pulsed Nd:YAG laser

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中国有色金属学会会刊：英文版 2009年第B09期19卷 157-163页

作者： Dong-Gyu ahn Gwang-Won JUNG Department of Mechanical Engineering Chosun University

The object of this work is to investigate the influence of process parameters on drilling characteristics of an Al 1050 sheet with a thickness of 0.2 mm using a pulsed Nd:YAG laser through numerical analyses and experiments. By comparing the numerical analyses with the experiments, a proper numerical model was obtained. From the results of the numerical analyses and the experiments, the effects of process parameters on entrance diameters of drilled holes, shapes of the holes, taper angles of the holes and temperature distributions in the vicinity of the holes were examined quantitatively. In addition, the optimal drilling condition was estimated to improve the quality of the drilled holes.

关键词： YAG激光器工艺参数 Nd 脉冲井用厚度色基数值分析

Zero-knowledge proofs of retrievability

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Science China(Information Sciences) 2011年第8期54卷 1608-1617页

作者： ahn Gail-Joon School of Computing Informatics and Decision Systems Engineering Arizona State University

Proof of retrievability (POR) is a technique for ensuring the integrity of data in outsourced storage *** this paper,we address the construction of POR protocol on the standard model of interactive proof *** propose the first interactive POR scheme to prevent the fraudulence of prover and the leakage of verified *** also give full proofs of soundness and zero-knowledge properties by constructing a polynomial-time rewindable knowledge extractor under the computational Diffie-Hellman *** particular,the verification process of this scheme requires a low,constant amount of overhead,which minimizes communication complexity.

关键词： cryptography integrity of outsourced data proofs of retrievability interactive protocol zero- knowledge soundness rewindable knowledge extractor

Influence of Processing Parameters on the Mechanical Properties of a Plasma Radical Nitrided SCM440 Steel

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Journal of Materials Science & Technology 2008年第3期24卷 356-358页

作者： Seok-Hwan ahn Insup Lee School of Mechanical Engineering Pukyong National University Department of Materials and Metallurgical Engineering Dongeui University

Plasma radical nitriding was performed to harden the surface of SCM440 steel for 1-10 h at temperature range of 450-550℃. This process involved the use of NH3 gas instead of N2 gas employed for the well-established plasma nitriding method. No compound layer was formed during this process except the experiment carried out at 500℃ for 10 h. The main phase produced in the diffusion zone was identified to be γ＇-Fe4（N, C）. A diffusion depth increased with increasing treatment temperature and time （up to about 250 μm）. The surface hardness of radical nitrided layer was about two times higher than that of the untreated surface. The tensile test was carried out to estimate the mechanical properties of surface-hardened SCM440 steel prepared at various plasma radical nitriding treatment time and temperature. The influence of radical nitriding treatment on the tensile strength of the specimen was found to be insignificant. The highest value of the ultimate tensile strength was obtained in the experiment carried out at 500℃ for 1 h. However, the elongation was greatly affected by the radical nitriding processing parameters. The maximum value of elongation, which is equal to about 18.1%, was also obtained under the condition of 500℃ for 1 h.

关键词： Plasma radical nitriding Tensile strength Elongation Surface hardness Diffusion depth Compound layer