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Enhanced thermoelectric performance of spark plasma sintered p-type Ca_(3-x)Y_(x)Co_(4)O_(9+δ)systems

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Journal of Materials Science & Technology 2020年第20期52卷 212-222页

作者： J.S.cha D.h.Kim h.Y.hong K.Park Faculty of Nanotechnology and Advanced Materials Engineering Sejong UniversitySeoul05006Republic of Korea

highly textured dense Ca3-xYxCo4 O9+δ(0≤x≤0.3)samples were fabricated by combining sol-gel process with spark plasma sintering(SPS).Y^3+substitution for Ca^2+simultaneously increased the Seebeck coefficient and reduced the thermal *** latter was attributed to the increase in lattice anharmonicity,structural distortion,and grain boundary area,which enhanced the phonon ***2.7Y0.3Co4 O9+δshowed the largest dimensionless figure-of-merit(ZT=0.194)at 1073 K because it had the largest Seebeck coefficient and the lowest thermal *** ZT value was 55%larger than that of undoped Ca3 Co4 O9(0.125 at 1073 K).Therefore,Y^3+substitution,sol-gel powder synthesis,and SPS are highly effective for enhancing the thermoelectric prope rties of Ca_(3)Co_(4)O_(9).

关键词： Electrical conductivity Ca_(3)Co_(4)O_(9) Thermoelectric properties Seebeck coefficient Thermal conductivity Spark plasma sintering

Suppression of pheromone biosynthesis and mating behavior by RNA interference of pheromone gland-specific fatty acyl reductase in Maruca vitrata

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Insect Science 2022年第4期29卷 1135-1144页

作者： Wook hyun cha Dae-Weon Lee Department of Biosafety Kyungsung UniversityBusanRepublic of Korea Metabolomics Research Center for Functional Materials Kyungsung UniversityBusanRepublic of Korea

In moths,various enzymes,such as fatty acid synthases,fatty acyl desaturases,and fatty acyl reductases(FARs),are involved in pheromone *** particular,pheromone gland-specific FAR(pgFAR)plays an important role in converting the functional group from carboxylic to alcohol during pheromone biosynthesis.A novel pgFAR of Maruca vitrata,Mvi-pgFAR,was identified through transcriptome sequencing of its pheromone *** investigate the involvement of Mvi-pgFAR in pheromone biosynthesis,Mvi-pgFAR was cloned from the pheromone gland and suppressed by RNA interference(RNAi).Mvi-pgFAR harbored several conserved motifs related to NAD(P)h-binding,N-glycosylation,and adenosine/guanosine triphosphate *** analysis revealed that Mvi-pgFAR with other lepidopteran pgFARs formed an independent ***-pgFAR was specifically expressed only in the pheromone *** real-time polymerase chain reaction showed that the diurnal expression levels of Mvi-pgFAR in the pheromone gland were the highest at 2 h before the *** primarily confirming Mvi-pgFAR suppression by RNAi,(E,E)-10,12-hexadecadienal(E10E12-16:Ald),a major sex pheromone component,was quantified by gas *** Mvi-pgFAR was successfully suppressed,E10E12-16:Ald production was reduced by up to half of that of the control,and the mating rate was subsequently *** results demonstrate that Mvi-pgFAR downregulation can suppress mating behavior by changing the relative sex pheromone component ratio,suggesting that Mvi-pgFAR can be used as a novel control target.

关键词： (EE)-10,12-hexadecadienal gas chromatography Maruca viruta pgFAR RNAi sex pheromone

Power hardware in the loop validation of fault ride through of VSC hVDC connected offshore wind power plants

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Journal of Modern Power Systems and Clean Energy 2014年第1期2卷 23-29页

作者： Ranjan ShARMA Qiuwei WU Seung Tae cha Kim h.JENSEN Tonny W.RASMUSSEN JacobØSTEGAARD Siemens Wind Power A/S Borupvej 167330 BranderDenmark Centre for Electric Power and Energy Department of Electrical EngineeringTechnical University of DenmarkElektrovej 3252800 Kongens LyngbyDenmark

This paper presents the power hardware in the loop(PhIL)validation of a feed forward DC voltage control scheme for the fault ride through(FRT)of voltage source converter(VSC)high voltage DC(hVDC)connected offshore wind power plants(WPPs).In the proposed FRT scheme,the WPP collector network AC voltage is actively controlled by considering both the DC voltage error and the AC current from the WPP AC collector system which ensures fast and robust FRT of the VSC hVDC connected offshore *** PhIL tests were carried out in order to verify the efficacy of the proposed feed forward DC voltage control scheme for enhancing the FRT capability of the VSC hVDC connected *** PhIL test results have demonstrated the proper control coordination between the offshore WPP and the WPP side VSC and the efficient FRT of the VSC hVDC connected WPPs.

关键词： Fault ride through high voltage DC(hVDC) Offshore wind power plant Power hardware in the loop(PhIL) Voltage source converter(VSC)

Leader-following consensus criteria for multi-agent systems with time-varying delays and switching interconnection topologies

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Chinese Physics B 2012年第11期21卷 144-153页

作者： M.J.Park O.M.Kwon Ju h.Park S.M.Lee E.J.cha School of Electrical Engineering Chungbuk National University Department of Electrical Engineering Yeungnam University School of Electronic Engineering Daegu University Department of Biomedical Engineering School of MedicineChungbuk National University

We consider multi-agent systems with time-varying delays and switching interconnection topologies. By con- structing a suitable Lyapunov-Krasovskii functional and using the reciprocally convex approach, new delay-dependent consensus criteria for the systems are established in terms of linear matrix inequalities （LMIs）, which can be easily solved by using various effective optimization algorithms. Two numerical examples are given to illustrate the effectiveness of the proposed methods.

关键词： consensus multi-agent systems time delay Lyapunov method

Synchronization criteria for coupled hopfield neural networks with time-varying delays

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Chinese Physics B 2011年第11期20卷 140-150页

This paper proposes new delay-dependent synchronization criteria for coupled hopfield neural networks with time-varying delays. By construction of a suitable Lyapunov Krasovskii＇s functional and use of Finsler＇s lemma, novel synchronization criteria for the networks are established in terms of linear matrix inequalities （LMIs） which can be easily solved by various effective optimization algorithms. Two numerical examples are given to illustrate the effectiveness of the proposed methods.

关键词： hopfield neural networks coupling delay synchronization Lyapunov method

Investigation of hot jet on active control of oblique detonation waves

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Chinese Journal of Aeronautics 2020年第3期33卷 861-869页

作者： hongbin LI Jianling LI cha XIONG Wei FAN Lei ZhAO Wenhu hAN School of Power and Energy Northwestern Polytechnical UniversityXi’an 710072China Shaanxi Key Laboratory of Internal Aerodynamics in Aero-Engine Xi’an 710072China State Key Laboratory of Explosion Science and Technology Beijing Institute of TechnologyBeijing 100081China

The hot jet injection is utilized to actively control the oblique detonation wave,such as initiating and stabilizing an oblique detonation wave at a desired position that is shorter than the length of induction zone,and adjust the height of the oblique detonation wave at the exit of combustor when the oblique detonation wave engine is working on off-design flight *** fifth order Weighted Essentially Non-Oscillatory(WENO)scheme and a two-step reversible reaction mechanism of the stoichiometric h_2/Air are adopted in the *** the help of hot jet injection,the transition from inert oblique shock wave to the oblique detonation wave immediately occurs near the position of hot jet injection,and consequently the length of combustor can be *** angle of oblique detonation wave also decreases as the hot jet injection approaches the nose of ***,the height of the oblique detonation wave at the exit of combustor can be flexibly adjusted,and also depends on the injection position and the strength of the hot *** the velocity of the hot jet is too weak to directly trigger the overall oblique detonation wave at the position of injection,increasing the injection pressure will improve the strength of the hot jet and results in a successful transition.

关键词： Active control hot jet Numerical simulation Oblique detonation wave Supersonic propulsion

h∞ synchronization of chaotic neural networks with time-varying delays

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Chinese Physics B 2013年第11期22卷 244-252页

作者： O. M. Kwon M. J. Park Ju h. Park S. M. Lee E. J. cha School of Electrical Engineering Chungbuk National University Department of Electrical Engineering Yeungnam University School of Electronic Engineering Daegu University Department of Biomedical Engineering School of Medicine Chungbuk National University

In this paper, we investigate the problem of h∞ synchronization for chaotic neural networks with time-varying delays. A new model of the networks with disturbances in both master and slave systems is presented. By constructing a suitable Lyapunov–Krasovskii functional and using a reciprocally convex approach, a novel h∞ synchronization criterion for the networks concerned is established in terms of linear matrix inequalities （LMIs） which can be easily solved by various effective optimization algorithms. Two numerical examples are given to illustrate the effectiveness of the proposed method.

关键词： chaotic neural networks time-varying delays h∞ synchronization Lyapunov method

Effects of homogenization temperature on microstructure and mechanical properties of high-speed-extruded Mg–5Bi–3Al alloy

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Journal of Magnesium and Alloys 2022年第10期10卷 2833-2846页

作者： Jae Won cha Sang-Cheol Jin Jae-Gil Jung Sung hyuk Park School of Materials Science and Engineering Kyungpook National University80 DaehakroDaegu 41566Republic of Korea Advanced Metals Division Korea Institute of Materials ScienceChangwon 51508Republic of Korea

This study investigates the effects of billet homogenization temperature on the dynamic recrystallization behavior during high-speed extrusion and resultant microstructure and tensile properties of the Mg–5Bi–3Al(BA53,wt%)*** billets homogenized at 350 and450℃(350h and 450h billets)are extruded at a high speed of 69 m/*** 350h billet has a relatively smaller grain size and a higher abundance of fine Mg3Bi2particles compared to the 450h *** extrusion of the 350h billet,enhanced dynamic recrystallization occurs as a result of its finer grains and abundance of particles,while the growth of recrystallized grains is suppressed by the grain-boundary pinning effect of ***,the extruded 350h material is characterized by smaller grains,relatively greater number of Mg3Bi2particles,and a higher internal strain energy than the extruded 450h *** tensile strength of the extruded 350h material is higher than that of the extruded 450h material owing to stronger grain-boundary hardening,particle hardening,and strain hardening *** extruded 350h material also exhibits a higher tensile elongation as its smaller grains inhibit the formation of crack-inducing undesirable twins during *** results from this study demonstrate that a decrease in the homogenization temperature from 450 to 350℃leads to improved strength and ductility in the high-speed-extruded BA53 material.

关键词： Mg–Bi–Al alloy high-speed extrusion homogenization Dynamic recrystallization Tensile properties

FUZZY REGRESSION MODEL TO PREDICT ThE BEAD GEOMETRY IN ThE ROBOTIC WELDING PROCESS

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Acta Metallurgica Sinica(English Letters) 2007年第6期20卷 391-397页

作者： B.S. Sung I.S. Kim Y. Xue h.h. Kim Y.h. cha Department of Material Engineering Chosun University 375 Seosul-Dong Dong-GuGwangju 501-759 Korea Department of Mechanical Engineering Mokpo National University 61 Dorim-riChungkye-Myun Muan-Gun Jconnam 534-729 Korea Department of Mechanical Engineering Chosun University 375 Seosul-Dong Dong-GuGwangju 501-759 Korea

Recently, there has been a rapid development in computer technology, which has in turn led to develop the fully robotic welding system using artificial intelligence （AI） technology. however, the robotic welding system has not been achieved due to difficulties of the mathematical model and sensor technologies. The possibilities of the fuzzy regression method to predict the bead geometry, such as bead width, bead height, bead penetration and bead area in the robotic GMA （gas metal arc） welding process is presented. The approach, a well-known method to deal with the problems with a high degree of fuzziness, is used to build the relationship between four process variables and the four quality characteristics, respectively. Using these models, the proper prediction of the process variables for obtaining the optimal bead geometry can be determined.

关键词： robotic arc welding bead geometry fuzzy regression modelwelding quality