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Study on Melting and Recrystallization of Poly(butylene succinate) Lamellar crystals via Step Heating Differential Scanning calorimetry

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chinese Journal of Polymer Science 2017年第12期35卷 1552-1560页

作者： Zhi-yu Lv michael c.zhang Yang zhang Bao-hua Guo 徐军 Key Laboratory of Advanced Materials (Ministry of Education) Department of Chemical Engineering Tsinghua University

Differential scanning calorimetry（DSc） has been widely applied to study crystallization and melting of materials. However, for polymeric lamellar crystals, the melting thermogram during heating process usually exhibits a broad endothermic peak or even multiple endotherms, which may result from changes of metastability via recrystallization process. Sometimes, the recrystallization exotherm cannot be observed due to its overlapping with the melting endotherm. In this work, we employed a step heating procedure consisting of successive heating and temperature holding stages to measure the metastability of isothermally crystallized poly（butylene succinate）（PBS） crystals. With this approach we could gain the fraction of crystals melted at different temperature ranges and quantitatively detect the melting-recrystallization behavior. The melting-recrystallization behavior depends on the polymer chain structure and the crystallization temperature. For instance, PBS block copolymer hardly shows recrystallization behavior while PBS oligomer and high molecular weight PBS homopolymer demonstrate remarkable melting-recrystallization phenomenon. High molecular weight PBS isothermally crystallized in the low temperature range shows multiple melting-recrystallization while those isothermally crystallized at elevated temperatures do not exhibit observable recrystallization behavior. Furthermore, the melting endotherms were fitted via the melting kinetics equations. The original isothermally crystallized lamellae demonstrate quite different melting kinetics from the recrystallized lamellar crystals that melt at the highest temperature range, which is attributed to the different degrees of stabilization. Finally, the mechanism of melting-recrystallization is briefly discussed. We propose that apparent meltrecrystallization phenomenon be observed when melting of preformed lamellar crystals and recrystallization of thicker lamellae have similar free energy barrier.

关键词： DSc Step heating Poly(butylene succinate) Metastability Melting-recrystallization Melting kinetics

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Small extracellular vesicles derived from cerebral endothelial cells with elevated microRNA 27a promote ischemic stroke recovery

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Neural Regeneration Research 2025年第1期20卷 224-233页

作者： Yi zhang Zhongwu Liu michael chopp michael Millman Yanfeng Li Pasquale cepparulo Amy Kemper chao Li Li zhang Zheng Gang zhang Department of Neurology Henry Ford HospitalDetroitMIUSA Department of Physics Oakland UniversityRochesterMIUSA Department of Pathology Henry Ford HospitalDetroitMIUSA Division of Pharmacology Department of NeuroscienceReproductive and Dentistry SciencesSchool of MedicineUniversity of Naples“Federico Ⅱ”NaplesItaly

Axonal remodeling is a critical aspect of ischemic brain repair processes and contributes to spontaneous functional *** previous in vitro study demonstrated that exosomes/small extracellular vesicles(sEVs)isolated from cerebral endothelial cells(cEc-sEVs)of ischemic brain promote axonal growth of embryonic cortical neurons and that microRNA 27a(miR-27a)is an elevated miRNA in ischemic *** the present study,we investigated whether normal cEc-sEVs engineered to enrich their levels of miR-27a(27a-sEVs)further enhance axonal growth and improve neurological outcomes after ischemic stroke when compared with treatment with non-engineered cEc-sEVs.27a-sEVs were isolated from the conditioned medium of healthy mouse cEcs transfected with a lentiviral miR-27a expression *** EVs isolated from cEcs transfected with a scramble vector(Scra-sEVs)were used as a *** male mice were subjected to permanent middle cerebral artery occlusion and then were randomly treated with 27a-sEVs or *** array of behavior assays was used to measure neurological *** with treatment of ischemic stroke with Scra-sEVs,treatment with 27a-sEVs significantly augmented axons and spines in the peri-infarct zone and in the corticospinal tract of the spinal grey matter of the denervated side,and significantly improved neurological *** vitro studies demonstrated that cEc-sEVs carrying reduced miR-27a abolished 27a-sEV-augmented axonal *** analysis revealed that 27a-sEVs systemically administered preferentially localized to the pre-synaptic active zone,while quantitative reverse transcription-polymerase chain reaction and Western Blot analysis showed elevated miR-27a,and reduced axonal inhibitory proteins Semaphorin 6A and Ras Homolog Family Member A in the peri-infarct *** of the clathrin-dependent endocytosis pathway substantially reduced neuronal internalization of *** data provide evidence that 27a-sEVs have

关键词： axonal remodeling cerebral endothelial cells exosomes miR-27a mitochondria Semaphorin 6A small extracellular vesicles stroke

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Limit of Spectral Resolution in Terahertz Time—Domain Spectroscopy

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chinese Physics Letters 2003年第8期20卷 1266-1268页

作者： JingzhouXu TaoYuan SamuelMickan X.-c.zhang centerforTHzResearch RensselaerPolytechnicInstituteTroyNY12180USA

The pulsed nature of terahertz time-domain spectroscopy (THz-TDS) sets a fundamental limit on its spectral resolution. The spectral resolution of THz-TDS can be improved by increasing the duration of the temporal measurement, but is limited by the dynamic range of the system in the time domain. This paper presents calculations and experimental results relating the temporal dynamic range of a THz-TDS system to its spectral resolution. We discuss three typical terahertz sources in terms of their dynamic range and hence achievable spectral resolution.

关键词： Terahertz spectroscopy

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Diffusion behavior at void tip and its contributions to void shrinkage during solid-state bonding

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Journal of Materials Science & Technology 2018年第8期34卷 1449-1454页

作者： c.zhang M.Q.Li H.Li School of Materials Science and Engineering Northwestern Polytechnical University State Key Laboratory of Solidification Processing Northwestern Polytechnical University Department of Mechanical Engineering University de Lyon

Solid-state diffusion bonding is an advanced joining technique, which has been widely used to join similar or dissimilar materials. Generally, it is easy to observe the diffusion behavior during dissimilar bonding, but for similar bonding the diffusion behavior has yet been observed via experiments. In this study, the diffusion behavior at void tip was firstly observed during similar bonding of stainless steel. Scanning electron microscopy with energy dispersive spectroscopy was used to examine the interface charac- teristic and diffusion behavior. The results showed that a diffusion region was discovered at void tip. Element concentrations of diffusion region were more than those of void region, but less than those of bonded region. This behavior indicated that the diffusion was ongoing at void tip, but the perfect bond has yet formed. The diffusion region was attributed to the interface diffusion from adjacent region to void tip due to the stress gradient along bonding interface. The mass accumulation at void tip transformed the sharp void tip into smooth one at the beginning of void shrinkage, and then resulted in shorter voids.

关键词： Stainless steel Micro-void morphology Solid-state bonding Void tip Element diffusion

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A route for large-scale preparation of multifunctional superhydrophobic coating with electrochemically-modified kaolin for efficient corrosion protection of magnesium alloys

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Journal of Magnesium and Alloys 2022年第11期10卷 3082-3099页

作者： Xiang Liu Tian c.zhang Yuxin zhang Jinsong Rao Shaojun Yuan Low-carbon Technology&chemical Reaction Engineering Lab College of Chemical EngineeringSichuan UniversityChengdu 610065China civil&Environmental Engineering Department University of Nebraska-LincolnOmahaNE 68182-0178USA State Key Laboratory of Mechanical Transmissions College of Materials Science and EngineeringChongqing UniversityChongqing 400044China

Superhydrophobic coating has been widely studied for its great applicational potential, such as for corrosion protection of magnesium alloys while it has been restrained by expensive materials, sophisticated preparation process and infirm rough structures. In this study, the electrochemical method was adopted by using a two-electrode system for rapid hydrophobic modification to obtain superhydrophobic *** mixing the modified superhydrophobic kaolin with commercial epoxy resin and polydimethylsiloxane glue, a paint can be formed and easily used on various substrates for preparation of superhydrophobic coating via spraying method. The influence factors on wettability of the modified kaolin and the mixing ratio of each component of the coating were explored. Also, the wettability, durability and anticorrosion of the prepared coating were evaluated comprehensively. The coating was able to maintain superhydrophobic after immersed in Hcl solution at pH 1, the NaOH solution at pH 14, and 3.5 wt.% Nacl solution for 16, 21, 30 days, respectively. In addition, the coating exhibited 4A grade adhesion, high hydrophobicity after abraded for 200 cycles on a 600-mesh sandpaper with 100 g weight, and 99.86% anticorrosion efficiency after soaked in 3.5 wt.% Nacl solution for 20 days, demonstrating a good robustness and anti-corrosion property. Furthermore, the coating showed good transparency, flexibility and was easy to make in a large scale by the spraying method, which is of great significance to promote the practical application of superhydrophobic coatings and the anticorrosion Mg alloys.

关键词： Superhydrophobic coating Large-scale application Magnesium alloys corrosion protection

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Binary doping of nitrogen and phosphorus into porous carbon: A novel di-functional material for enhancing cO_(2) capture and super-capacitance

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Journal of Materials Science & Technology 2022年第4期99卷 73-81页

作者： Yuan Wang Jianfei Xiao Hanzhi Wang Tian c.zhang Shaojun Yuan Low-carbon Technology&chemical Reaction Engineering Lab College of Chemical EngineeringSichuan UniversityChengdu 610065China civil&Environmental Engineering Department University of Nebraska-LincolnOmahaNE 68182-0178USA

Designing of hetero-atomic doped carbon-based systems through pyrolysis of abundant element organic precursors is a novel approach to construct rational porous carbon ***,a highly-cross-linked triazine polymer is employed to fabricate N,P co-doped porous carbon(A-TDP-12)with tunable active nitrogen in the carbon framework for simultaneous enhancement of cO_(2) capture capability and Supercapacitance(Sc).The synthesized A-TDP-12 possesses a typical hierarchically porous framework(micro-pores and meso-pores)with a large surface area(1332 m^(2) g^(-1))and a rich content of N(7.89 at.%)and P(0.74 at.%).It delivers a cO_(2) adsorption capacity of 1.52 and 5.68 mmol g^(-1) at 1 and 5 bar,respectively,with almost no decay after successive 8 *** 6 M KOH aqueous electrolyte,A-TDP-12 exhibits a superior specific capacitance of 172.7 F g^(-1) at a current density of 1 A g^(-1).Even at a high current density of 10 A g^(-1),80%of its initial capacity still *** work not only offers a novel strategy for fabricating promising adsorbents and electrodes for cO_(2) uptake and Scs,but also provides new insights into design of porous carbon material for related applications.

关键词： N,P co-doping Porous carbon cO_(2)capture Super-capacitors Bi-function

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The Kirkendall effect on erosion resistance of chrome-coated 25cr3Mo2WNiV and 30SiMn2MoV gun barrel steels

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Journal of Materials Science & Technology 2024年第10期177卷 246-255页

作者： c.H.Dou P.F.Jin c.Z.Wang J.J.Li c.zhang J.F.Huang c.zhang Key Laboratory for Advanced Materials Processing State State Key Laboratory for Advanced Metals and MaterialsUniversity of Science and Technology BeijingBeijing 100083China National Joint Engineering Research center for Abrasion control and Molding of Metal Materials School of Materials Science and EngineeringHenan University of Science and TechnologyLuoyang 471003China

This study aimed to investigate the erosion behavior and mechanism of a newly developed 25cr3Mo2WNiV steel with a chrome coating using promoted ignition combustion *** erosion threshold pressure and temperature of the chrome-coated 25cr3Mo2WNiV steel were determined to be 0.2 MPa and 254.3 K higher than those of traditional chrome-coated 30SiMn2MoV ***,Kirkendall voids and inter-diffusion between the cr coating and matrix were first observed before *** improved erosion resistance of the chrome-coated 25cr3Mo2WNiV steel was attributed to the suppression of the Kirkendall effect,which minimized heat generation at the cr/matrix interface by pre-venting oxygen diffusion and reducing oxygen affinity.

关键词： Erosion resistance Kirkendall effect cr coating Gun steel

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Preparation of silver nanoparticles through the reduction of straw-extracted lignin and its antibacterial hydrogel

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International Journal of Minerals,Metallurgy and Materials 2025年第2期32卷 504-514页

作者： Lou zhang Shuo Li Fu Tang Jingkai zhang Yuetong Kang Hean zhang Lidong Li State Key Laboratory for Advanced Metals and Materials School of Materials Science and EngineeringUniversity of Science and Technology BeijingBeijing 100083China

Silver nanoparticles(Ag NPs)have attracted attention in the field of biomaterials due to their excellent antibacterial ***,the reducing and stabilizing agents used for the chemical reduction of Ag NPs are usually toxic and may cause water *** this work,Ag NPs(31.2 nm in diameter)were prepared using the extract of straw,an agricultural waste,as the reducing and stabilizing *** analysis revealed that the straw extract contained lignin,the structure of which possesses phenolic hydroxyl and methoxy groups that facilitate the reduction of silver salts into Ag *** surfaces of Ag NPs were negatively charged due to the encapsulation of a thin layer of lignin molecules that prevented their *** the prepared Ag NPs were added to the precursor solution of acrylamide,free radical polymerization was triggered without the need for extra heating or light irradiation,resulting in the rapid formation of an Ag NP-polyacrylamide composite *** inhibition zone test proved that the composite hydrogel possessed excellent antibacterial ability due to the presence of Ag *** prepared hydrogel may have potential applications in the fabrication of biomedical materials,such as antibacterial dressings.

关键词： silver nanoparticles hydrogel straw extraction antibacterial

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Depression mechanism of sulfite ions on sphalerite and Pb^(2+)activated sphalerite in the flotation separation of galena from sphalerite

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International Journal of Minerals,Metallurgy and Materials 2025年第2期32卷 335-345页

作者： Feng zhang chenyang zhang Linlin Wu Wei Sun Hongliang zhang Jianhua chen Yong Pei Songjiang Li Engineering Research center of Ministry of Education for carbon Emission Reduction in Metal Resource Exploitation and Utilization Hunan International Joint Research Center for Efficient and Clean Utilization of Critical Metal Mineral ResourcesSchool of Minerals Processing and BioengineeringCentral South UniversityChangsha 410083China State Key Laboratory of Mineral Processing Beijing General Research Institute of Mining&MetallurgyBeijing 100160China Hunan Provincial Key Laboratory of Micro&Nano Materials Interfaces Science College of Chemistry and Chemical EngineeringCentral South UniversityChangsha 410083China School of Resources Environment and MaterialsGuangxi UniversityNanning 530004China Department of chemistry Xiangtan UniversityXiangtan 411105China china Railway Resource Group co.Ltd Beijing 102300China

The depression mechanism of sulfite ions on sphalerite and Pb^(2+)activated sphalerite in the flotation separation of galena from sphalerite still lacked in-depth ***,the depression mechanism of sulfite ions on sphalerite and Pb^(2+)activated sphalerite in the flotation separation of galena from sphalerite was further systematically investigated with experiments and density functional theory(DFT)*** X-ray photoelectric spectroscopy(XPS)results,DFT calculation results,and frontier molecular orbital analysis indicated that sulfite ions were difficult to be adsorbed on sphalerite surface,suggesting that sulfite ions achieved depression effects on sphalerite through other non-adsorption ***,the oxygen content in the surface of sphalerite treated with sulfite ions in creased,which enhanced the hydrophilicity of the sphalerite and further increased the difference in hydrophilicity between sphalerite and ***,sulfite ions were chelated with lead ions to form PbSO_(3)in *** hydrophilic PbSO_(3)was more easily adsorbed on sphalerite than *** interaction between sulfite ions and lead ions could effectively inhibit the activation of *** addition the UV spectrum showed that after adding sulfite ions,the peak of perxanthate in the sphalerite treated xanthate solution was significantly stronger than that in the galena with xanthate solution,indicating that xanthate interacted more readily with sulfite ions and oxygen mo lecules within the sphalerite system,leading to the formation of ***,sulfite ions hardly depressed the flotation of ga lena and could promote the flotation of galena to some *** study deepened the understanding of the depression mechanism o sulfite ions on sphalerite and Pb^(2+)activated sphalerite.

关键词： sphalerite galena sulfite ion density functional theory depression mechanism

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GPcR activation:protonation and membrane potential

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Protein & cell 2013年第10期4卷 747-760页

作者： Xuejun c.zhang Kening Sun Laixing zhang Xuemei Li can cao National Laboratory of Macromolecules National Center for Protein Science-BeijingInstitute of BiophysicsChinese Academy of SciencesBeijing 100101China

GPcR proteins represent the largest family of signaling membrane proteins in eukaryotic *** importance to basic cell biology,human diseases,and pharma-ceutical interventions is well *** crystal structures of GPcR proteins have been reported in both active and inactive *** data indicate that agonist binding alone is not suffi cient to trigger the conformational change of GPcRs necessary for binding of downstream G-proteins,yet other essential factors re-main *** on analysis of available GPcR crystal structures,we identifi ed a potential conformational switch around the conserved Asp2.50,which consistently shows distinct conformations between inactive and active *** the structural information with the current literature,we propose an energy-coupling mechanism,in which the interaction between a charge change of the GPcR protein and the membrane potential of the living cell plays a key role for GPcR activation.

关键词： GPcR membrane potential protonation ac-tivation

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