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CRYSTALLIZATION CHARACTERISTICS OF β-PHASE CRYSTALS IN COPOLYMERS OF POLYPROPYLENE WITH LOW ETHYLENE CONTENT

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Chinese Journal of Polymer Science 2001年第3期19卷 317-322页

作者： Wen-tao Hao Yi-yong He Xiao-lie Luo de-zhu ma department of Polymer Science and Engineering University of Science and Technology of China Hefei 230026 China Univ Sci & Technol China Dept Polymer Sci & Engn Hefei 230026 Peoples R China

Polypropylene copolymers (CPP) containing β-nucleating agent were investigated by differential scanningcalorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarizing light microscopy (PLM). The results show thathigh content of β-phase crystals can also be formed for CPPs. Like PP homopolymers, the CPPs also have a most favorabletemperature near 132℃ for β-phase crystal growth. The crystallization rate of CPPs containing β-nucleating agent (β-CPP) ismuch greater than that of PP homopolymer containing β-nucleating agent (β-PP homopolymer). The observation ofspherulite morphology of β-CPP and β-PP homopolymer shows that the spherulites of β-CPP are more imperfect than thoseof β-PP homopolymer.

关键词： Copolymer polypropylene β-Nucleating agent Differential scanning calorimetry Wide angle X-ray diffraction Spherulite

TRANSESTERIFICATION OF POLY(ETHYLENE TEREPHTHALATE) WITH POLY(ε-CAPROLACTONE)

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Chinese Journal of Polymer Science 2000年第5期18卷 405-412页

作者： Zheng-ping Zhang Xiao-lie Luo Yu-chen Lu de-zhu ma department of Polymer Science and Engineering, University of Science and Technology of China, Hefei 230026, China Univ Sci & Technol China Dept Polymer Sci & Engn Hefei 230026 Peoples R China

Transesterification of poly（ethylene terephthalate）（PET） with poly（ε-caprolactone）（PCL） was investigated bymeans of NMR spectroscopy, extraction experiments, differential scanning calorimetry （DSC） and phase contrast microscopy（PCM）. The;H-NMR results show that transesterification takes place in the melt blends and leads to the formation of thePET-PCL copolyester with a chemical structure similar to ethylene terephthalate-ε-caprolactonc copolycster （TCL）synthesized directly from monomers. However, even in the blend that has been transesterified for 8 h, the random PET-PCLcopolyester, PET-PCL copolyester with long PET or long PCL segments and the unreacted PET and PCL homopolymersmay coexist. Due to the low mobility of PET and PCL chains and the high viscosity of the two macromolecules, thetransesterification proceeds with difficulty. Furthermore, PET is incompatible with PCL, the transesterification can onlyoccur at the interface or in the interfacial region between two phases, and finally the reaction can only reach a localequilibrium. These results indicate that in fact the transesterification in the melt blend between two incompatiblehomopolymers could not lead to the formation of completely random or typical block copolyesters.

关键词： Transesterification Poly(ethylene terephthalate) Poly(ε-caprolactone) Crystallization Phase structure

ATOMIC FORCE MICROSCOPY STUDIES OF POLYCAPROLACTONE RINGED SPHERULITES

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Chinese Journal of Polymer Science 2000年第6期18卷 569-572页

作者： Jian-bin Zhang de-zhu ma Hua Zhong Xiao-lie Luo department of Polymer Science and Engineering, University of Science and Technology of China, Hefei 230026, China Univ Sci & Technol China Dept Polymer Sci & Engn Hefei 230026 Peoples R China

The surface morphology of free-surface PCL ringed spherulites was investigated by using atomic force microscopy. The spherulites were obtained by crystallization of PCL/PVC blends of different compositions. It was found that the ringed spherulite exhibited regularly fluctuating rings on its surface. Compared with the bright-dark ring pattern of the spherulite under a polarizing microscope, it was proved that the optical characteristics of the ringed spherulite under polarizing microscope coincided with its surface characteristics. The bright rings in polarizing micrographs of the spherulite coincided with the convex rings on its surface, while the dark rings coincided with the concave rings.

关键词： AFM surface morphology ringed spherulites PCL/PVC blends

Measuring Financial Systemic Risk:Net Liability Clearing Mechanism and Contagion Effect

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Journal of Systems Science & Complexity 2024年第3期37卷 1114-1146页

作者： ma Jiali zhu Shushang LI Duan College of Big Data Statistics Guizhou University of Finance and EconomicsGuiyang 550025China School of Business Sun Yat-Sen UniversityGuangzhou 510275China School of Data Science City University of Hong KongHong Kong 999077China

Following the framework of E-N model(Eisenberg and Noe,2001),the authors consider a new clearing mechanism based on net liabilities among financial institutions since the liabilities between the counterparties should be deducted accordingly when clearing in *** the basis for systemic risk measurement,similar to the original E-N model,the authors first establish some good properties for the clearing payment vector according to a more general ***,the authors investigate how risk spreads among institutions through the liability network forming the risk contagion ***,the authors illustrate with a specific example that the original E-N clearing mechanism may misidentify the systemic important institutions,and theoretically show that it may also overestimate the risk compared with the netting clearing mechanism.

关键词： Clearing mechanism contagion net liability network systemic risk

L^(*)—An index for evaluating long range performance of autonomous underwater vehicles(AUVs)

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Friction 2024年第10期12卷 2205-2221页

作者： manfu zhu Liran ma Jianbin LUO State Key Laboratory of Tribology in Advanced Equipment Tsinghua UniversityBeijing 100084China

Autonomous underwater vehicles(AUVs)have various applications in both military and civilian fields.A wider operation area and more complex tasks require better overall range performance of ***,until recently,there have been few unified criteria for evaluating the range performance of *** the present work,a unified range index,i.e.,L^(*),considering the cruising speed,the sailing distance,and the volume of an AUV,is proposed for the first time,which can overcome the shortcomings of previous criteria using merely one single parameter,and provide a uniform criterion for the overall range performance of various *** constructing the expression of the L^(*)index,the relevant data of 49 AUVs from 12 countries worldwide have been collected,and the characteristics of the L^(*)range index in different countries and different categories were compared and ***,by analyzing the complex factors affecting the range index,methods to enhance the L^(*)range index value,such as efficiency enhancement and drag reduction,have been introduced and *** this condition,the work proposes a unified and scientific criterion for evaluating the range performance of AUVs for the first time,provides valuable theoretical insight for the development of AUVs with higher performance,and then arouses more attention to the application of the cutting-edge superlubricity technology to the field of underwater vehicles,which might greatly help to accelerate the coming of the era of the superlubricitive engineering.

关键词： autonomous underwater vehicles(AUVs) range performance range index superlubricity drag reduction

THERmaLLY STIMULATED SHAPE MEMORY BEHAVIOR OF(ETHYLENE OXIde-BUTYLENE TEREPHTHALATE)SEGMENTED COPOLYMER

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Chinese Journal of Polymer Science 2000年第4期18卷 357-361页

作者： Xiao-lie Luo Ming-chuan Zhao Mo-zhen Wang Lu-na Ding de-zhu ma department of Polymer Science and Engineering, University of Science and Technology of China, Hefei 230026, China Univ Sci & Technol China Dept Polymer Sci & Engn Hefei 230026 Peoples R China

The thermally stimulated shape memory behavior of ethylene oxide-butylene terephthalate (EOBT) segmented copolymers with different soft segment molecular weight and hard segment content was investigated. The deformation recovery ratio R-f of the EOBT samples increases with the soft segment molecular weight and the hard segment weight content, while the average overall deformation recovery speed V-r increases with the hard segment content. The temperature of maximum deformation recovery speed (T-M) is determined by the melting temperature of the soft segment crystals and the stability of the crystallized hard segment domains.

关键词： ethylene oxide-butylene terephthalate segmented copolymers shape memory crystallized hard segment

Review on heat-to-power conversion technologies for hypersonic vehicles

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Chinese Journal of Aeronautics 2024年第5期37卷 148-179页

作者： Yinke QI Xiaofeng ma Peixue JIANG Yinhai zhu Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Department of Energy and Power EngineeringTsinghua UniversityBeijing 100084China Beijing Key Laboratory of CO_(2)Utilization and Reduction Technology Department of Energy and Power EngineeringTsinghua UniversityBeijing 100084China

Hypersonic vehicles have enormous military and economic value,while their power and thermal protection demands will increase substantially with the rise in mach number and *** the tremendous high-quality heat on the vehicle surface and engine wall into electrical energy through heat-to-power technologies will not only play a role in thermal protection,but also supply power for the *** paper provides a comprehensive review of heat-to-power conversion technologies on hypersonic vehicles,including the indirect conversion of Brayton and Rankine cycles,direct conversion of thermoelectric materials,and combined *** the open Brayton cycle with hydrocarbon fuel as the working fluid,the Power-to-Weight Ratio(PWR)can achieve the highest,at around 1.8,due to the high PWR of the hydrocarbon fuel turbine and the few components of the ***,its work capacity is limited by the flow rate of the supplied *** closed Brayton cycle can maintain a relatively high PWR,ranging from 0.2 to 0.8,while achieving relatively high output power and conversion *** Rankine cycle has a higher PWR,its range is close to that of the closed Brayton cycle,peaking at about *** thermoelectric materials technology has a small power generation level,making it more suitable for scenarios with low power *** review provides a basis for selecting and developing heat-to-power conversion technologies on hypersonic vehicles.

关键词： Hypersonic vehicles Heat-to-power conversion Brayton cycle Rankine cycle Thermoelectric materials

Two simple memristive maps with adaptive energy regulation and digital signal process verification

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2024年第5期25卷 382-394页

作者： Feifei YANG Lujie REN Jun ma Zhigang zhu College of Electrical and Information Engineering Lanzhou University of TechnologyLanzhou 730050China department of Physics Lanzhou University of TechnologyLanzhou 730050China School of Information Science and Engineering Dalian Polytechnic UniversityDalian 116034China

mathematical models can produce desired dynamics and statistical properties with the insertion of suitable nonlinear terms,while energy characteristics are crucial for practical application because any hardware realizations of nonlinear systems are relative to energy *** involvement of memristive terms relative to memristors enables multistability and initial-dependent property in memristive *** this study,two kinds of memristors are used to couple a capacitor or an inductor,along with a nonlinear resistor,to build different neural *** corresponding circuit equations are derived to develop two different types of memristive oscillators,which are further converted into two kinds of memristive maps after linear *** Hamilton energy function for memristive oscillators is obtained by applying the Helmholz theorem or by mapping from the field energy of the memristive *** Hamilton energy functions for both memristive maps are obtained by replacing the gains and discrete variables for the memristive oscillator with the corresponding parameters and *** two memristive maps have rich dynamic behaviors including coherence resonance under noisy excitation,and an adaptive growth law for parameters is presented to express the self-adaptive property of the memristive maps.A digital signal process(DSP)platform is used to verify these *** scheme will provide a theoretical basis and experimental guidance for oscillator-to-map transformation and discrete map-energy calculation.

关键词： Hamilton energy Discrete memristor Self-adaptive regulation Digital signal process(DSP)implementation

Effect of heat treatment on the microstructure,mechanical properties and fracture behaviors of ultra-high-strength SiC/Al-Zn-Mg-Cu composites

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International Journal of Minerals,Metallurgy and materials 2024年第10期31卷 2233-2243页

作者： Guonan ma Shize zhu Dong Wang Peng Xue BolüXiao Zongyi ma Shi-changxu Innovation Center for Advanced materials Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China Centre of Excellence for Advanced materials Dongguan 523808China

A high-zinc composite,12vol%SiC/Al-13.3 Zn-3.27 Mg-1.07Cu(wt%),with an ultra-high-strength of 781 MPa was success-fully fabricated through a powder metallurgy method,followed by an extrusion *** effects of solid-solution and aging heat treat-ments on the microstructure and mechanical properties of the composite were extensively *** with a single-stage sol-id-solution treatment,a two-stage solid-solution treatment(470℃/1 h+480℃/1 h)exhibited a more effective solid-solution strengthen-ing owing to the higher degree of solid-solution and a more uniform *** to the aging hardness curves of the com-posite,the optimized aging parameter(100℃/22 h)was *** the aging temperature and time resulted in finer and more uniform nanoscale precipitates but only yielded a marginal increase in tensile *** fractography analysis revealed that intergranu-lar cracking and interface debonding were the main fracture mechanisms in the ultra-high-strength SiC/Al-Zn-Mg-Cu *** regions,such as the SiC/Al interface containing numerous compounds and the precipitate-free zones at the high-angle grain boundaries,were identified as significant factors limiting the strength enhancement of the *** compounds,including MgO,MgZn2,and Cu5Zn8,reduced the interfacial bonding strength,leading to interfacial debonding.

关键词： metal matrix composites heat treatment interfacial reaction mechanical properties fracture mechanism