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Creep deformation and strength evolution mechanisms of a Ti-6Al-4V alloy during stress relaxation at elevated temperatures from elastic to plastic loading

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Journal of Materials science & Technology 2022年第31期126卷 93-105页

作者： Ying Zhang Dongsheng Li Xiaoqiang Li Xiaochun Liu Shiteng Zhao Yong Li School of Mechanical Engineering and Automation Beihang UniversityBeijing 100191China Institute of Metals College of Materials Science and EngineeringChangsha University of Science&TechnologyChangsha 410004China School of Materials science and Engineering Beihang UniversityBeijing 100191China

In this study, the stress relaxation(SR) behaviors of a Ti-6Al-4V alloy pre-loaded from elastic to plastic regions and corresponding strength evolution mechanisms at different temperatures were systematically studied. In order to quantitatively analyze the detailed deformation and strength evolution mechanisms during the whole SR tests, which is composed of the loading stage and subsequent SR stage, the evolutions of α/β structures and dislocations have been identified by a series of microstructural observations,i.e., scanning electron microscopy(SEM), electron backscatter diffraction(EBSD), high resolution transmission electron microscopy(HRTEM), energy dispersive spectroscopy(EDS). A great quantity of entangled dislocations in α phase introduced by the plastic loading at temperatures below 800 °C promotes the emergence of SR behavior with a higher creep rate, leading to the much higher SR level with larger pre-load levels. Diffusion is significantly enhanced by dislocations accumulated at interfaces with higher temperatures(> 800 ℃), contributing to a similar SR phenomenon under different initial strain *** strength loss has been observed after SR with high temperatures or pre-loaded to the plastic region, e.g., 94 MPa loss for 800 °C, pre-loaded with a stain of 10% and SR for 2400 s. The strength loss mainly comes from the loading stage where distorted and fragmented β layers occur. The subsequent SR stage facilitates interfacial diffusion and results in a higher fraction of granular β phases, leading to a further decrease in yield strength(YS). This study enhances the understanding on the deformation and strength evolution mechanisms of titanium alloys with lamellar structures in the whole SR process, providing a physical foundation for optimizing the processing parameters for manufacturing titanium alloy components with high accuracy and performance.

关键词： Stress relaxation Initial strain Ti-6Al-4V Yield strength Dislocation density

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Interfacial reaction between oxide inclusion and steel matrix deoxidized by Si and Mn at 1473 K

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Journal of Iron and Steel Research International 2018年第1期25卷 1-8页

作者： Xue-liang Zhang Shu-feng Yang Cheng-song Liu Jing-she Li Qing Liu Gang Liu School of Metallurgical and Ecological Engineering University of Science and Technology BeijingBeijing 100083 China Beijing Key Laboratory of Special Melting and Preparationof High-End Metals Beijing 100083 China The State Key Laboratory of Refractories and MetallurgyWuhan University of science and Technology Wuhan 430081 Hubei China

An improved diffusion couple method was used to simulate the dynamic process of the solid-state reaction at the interface between oxide inclusions and a steel matrix deoxidized by Si and Mn during heat treatment at 1473 K. Experimental results indicated that good contact between the oxide and steel matrix was attained after pre-treatment at 1673 K. In addition, the reaction between the oxide and steel matrix at 1673 K was suppressed, and the effect of this reaction on the diffusion couple experiments at 1473 K was minimized. In the diffusion couple experiments, the diffusion of oxygen from the oxide to the steel matrix resulted in the precipitation of fine oxide particles and a decrease in the Mn content in the steel matrix near the interface after heat treatment at 1473 K. With increasing heat treatment time, the widths of the particle precipitation zone （PPZ） and Mn-depleted zone （MDZ） gradually increased. In addition, the solid-state reaction at the interface between the oxide and steel matrix was intense, and the widths of the PPZ and MDZ increased rapidly during the 0-20 h stage of heat treatment, especially during the 0-5 h stage. The interfacial reaction was retarded, and the rates of width expansion of PPZ and MDZ decreased with increasing heat treatment time.

关键词： Oxide inclusion Diffusion couple Heat treatment Solid-state reaction Interfacial reaction

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Co-infection of Wolbachia and Spiroplasma in spider mite Tetranychus truncatus increases male fitness

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Insect science 2020年第5期27卷 921-937页

作者： Kang Xie Yi-Jia Lu Kun Yang Shi-Mei Huo Xiao-Yue Hong Department of Entomology Nanjing Agricultural UniversityNanjingChina

Wolbachia and Spiroplasma are intracellular bacteria that are of great interest to entomologists,because of their ability to alter insect host biology in multiple *** the spider mite Tetranychus truncatus,co-infection of Wolbachia and Spiroplasma can induce cytoplasmic incompatibility(CI)and fitness costs;however,lttle is known about the effect of co-infection at the genetic level and the molecular mechanisms underlying *** this study,we explored the influence of the two symbionts on male mite host fitness and used RNA sequencing to generate the transcriptomes of T truncatus with four different types of *** total,we found symbiont-infected lines had a higher hatch proportion than the uninfected line,and the development time of the uninfected line was longer than that of the other ***-infection changed the expression of many genes related to digestion detoxification,reproduction,immunity and oxidation *** results indicate that co-infection of Wolbachia and Spiroplasma confers multiple effects on their hosts,and helps iluminate the complex interactions between endosymbionts and arthropods.

关键词： co-infection development time Spiroplasma Tetranychus truncatus tran-scriptome Wolbachia

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Enhanced comprehensive properties of directed energy deposited Inconel 718 by a novel integrated deposition strategy

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Journal of Materials science & Technology 2023年第10期141卷 42-55页

作者： Naiyuan Xi Kexin Tang Xuewei Fang Yan Li Yusong Duan Ke Huang The State Key Laboratory for Manufacturing Systems Engineering Xi’an Jiaotong UniversityXi’an 710054China

Nickel-based superalloys fabricated by wire-arc directed energy deposition,also known as wire arc ad-ditive manufacturing(WAAM),usually exhibit inherent columnar grain structure,micro-segregation,and rough surface.A novel deposition strategy,integrating an oscillating arc and forced interlayer cooling,was developed in WAAM of Inconel(IN)718 *** influences of deposition modes on geometrical characteristics,defects,microstructure,and mechanical properties were systematically *** re-sults showed that the oscillation mode,compared to the standard parallel mode,can effectively promote the molten pool’s spread and wettability,as well as prevent overflow,finally resulting in high geometric *** addition,the voids-like defects were reduced by 77.78%,while most common crack defects were not ***,the forced interlayer cooling process further increased the cooling rate,leading to the reduction of the element segregation as well as the proportion of long-chain-like Laves *** a short-process modified heat treatment,the anisotropic mechanical behaviors of the as-deposited samples were almost *** with the parallel mode samples,the yield strength and ultimate tensile strength of the oscillation path samples increased by 5.75%and 9.25%,respectively,while the elongation increased significantly by 51.20%.This signifies that their strength and ductility were simultaneously *** strengthening mechanisms were further analyzed based on the distribution of the strengthening phases,as well as the residual Laves phases and porosity.

关键词： Wire arc additive manufacturing Deposition strategy Microstructure characterization Strengthening mechanism Inconel 718

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The role of refocusing in dynamic X-wave formation during femtosecond laser filamentation in water

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Chinese Optics Letters 2010年第2期8卷 244-247页

作者：徐俊杰徐晗熊辉程亚徐至展刘伟伟陈瑞良 State Key Laboratory of High Field Laser Physics Shanghai Institute of Optics and Fine MechanicsChinese Academy of Sciences Key Laboratory of Opto-Electronic Information science and Technology Centre d'Optique Photonique er Laser(COPL)and Departement de Physiquede Genie Physique et d'OptiqueUniversite LavalQuebec

With the evolution of a laser pulse in water, the formation of a nonlinear X wave during femtosecond filamentation is investigated based on numerical simulations. In particular, we analyze the far-field angularly resolved spectra obtained for different temporal portions of the ultrashort pulse during its propagation. Our result shows that the refocusing of ultrashort pulse leads to the formation of dynamic X wave which essentially manifests itself as conical emission.

关键词： Acoustic waves Computer simulation Light propagation Ultrashort pulses

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A hydrodynamic model of loop seal with a fluidized standpipe for a circulating fluidized bed

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Particuology 2018年第1期16卷 50-58页

作者： Changjin Li Zheng ZOU Hongzhong Li Qingshan Zhu State Key Laboratory of Multi-phase Complex Systems Institute of Process Engineering Chinese Academy of Sciences Beijing 100190 China University of Chinese Academy of sciences Beijing 100049 China

Loop seals are among the most common non-mechanical valves used in circulating fluidized bed sys- tems. In the present work. a fundamental study is conducted of a fluidized loop seal, which consists of a fluidized standpipe, a fluidized supply chamber, and a fluidized recycling chamber. Based on the princi- ples of momentum, mass. and energy conservation, a hydrodynamic model for a loop seal is established, consisting of 13 equations. The effects of operating conditions such as the bottom aeration rate, total solid inventory, and fluidizing gas velocity in the riser on the solids flow rate and the performance of the loop seal are studied by a combination of model analysis and experiments. The experiments are carried out in a circulating fluidized bed with silica gel particles （Geldart group A）. The model predictions show good agreement with the experimental data.

关键词： Circulating fluidized bed Loop seal Hydrodynamic model

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On the improvement of signal repeatability in laser-induced air plasmas

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Frontiers of physics 2018年第2期13卷 85-92页

作者： Shuai Zhang Sahar Sheta Zong-Yu Hou Zhe Wang Department of Thermal Engineering Tsinghua-BP Clean Energy Center Tsinghua University Beijing 100084 China national Institute of Laser Enhanced science Cairo University Cairo 12613 Egypt

The relatively low repeatability of laser-induced breakdown spectroscopy （LIBS） severely hinders its wide commercialization. In the present work, we investigate the optimization of LIBS system for repeatability improvement for both signal generation （plasma evolution） and signal collection. Time- integrated spectra and images were obtained under different laser energies and focal lengths to inves- tigate the optimum configuration for stable plasmas and repeatable signals. Using our experimental setup, the optimum conditions were found to be a laser energy of 250 mJ and a focus length of 100 ram. A stable and homogeneous plasma with the largest hot core area in the optimum condition yielded the most stable LIBS signal. Time-resolved images showed that the rebounding processes through the air plasma evolution caused the relative standard deviation （RSD） to increase with laser energies of 〉 250 mJ. In addition, the emission collection was improved by using a concave spherical mirror. The line intensities doubled as their RSDs decreased by approximately 25%. When the signal generation and collection were optimized simultaneously, the pulse-to-pulse RSDs were reduced to approximately 3% for O（I）, N（I）, and H（I） lines, which are better than the RSDs reported for solid samples and showed great potential for LIBS quantitative analysis by gasifying the solid or liquid samples.

关键词： laser-induced breakdown spectroscopy (LIBS) repeatability air-plasma signalfluctuations plasma evolution

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The Structure and Bifurcation of Atmospheric Motions

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Advances in Atmospheric sciences 2004年第4期21卷 557-561页

作者：刘式适刘式达付遵涛辛国君梁福明 School of Physics Peking University Beijing 100871 School of Physics Peking University Beijing 100871 State Key Laboratory for Turbulence and Complex Systems Peking University Beijing 100871 School of Physics Peking University Beijing 100871he 3-D spiral structure resulting from the balance between the pressure gradient force Coriolis force and viscous force is a common atmospheric motion pattern. If the nonlinear advective terms are considered this typical pattern can be bifurcated. It is shown that the surface low pressure with convergent cyclonic vorticity and surface high pressure with divergent anticyclonic vorticity are all stable under certain conditions. The anomalous structure with convergent anticyclonic vorticity is always unstable. But the anomalous weak high pressure structure with convergent cyclonic vorticity can exist and this denotes the cyclone's dying out.

The 3-D spiral structure resulting from the balance between the pressure gradient force, Coriolis force, and viscous force is a common atmospheric motion pattern. If the nonlinear advective terms are considered, this typical pattern can be bifurcated. It is shown that the surface low pressure with convergent cyclonic vorticity and surface high pressure with divergent anticyclonic vorticity are all stable under certain conditions. The anomalous structure with convergent anticyclonic vorticity is always unstable. But the anomalous weak high pressure structure with convergent cyclonic vorticity can exist, and this denotes the cyclone’s dying out.

关键词： horizontal divergence vertical vorticity spiral structure bifurcation

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Fabrication of AQ2S/GR composite photosensitizer for the simulated solar light-driven degradation of sulfapyridine

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Environmental science and Ecotechnology 2021年第4期8卷 1-9页

作者： Shuang-Yang Zhao Cheng-Xin Chen Jie Ding Shan-Shan Yang Ya-Ni Zang Xu-Dong Qin Xin-Lei Gao Zhao Song Nan-Qi Ren State Key Laboratory of Urban Water Resource and Environment School of EnvironmentHarbin Institute of TechnologyHarbin150090China Harbin Institute of Technology national Engineering Research Center of Water Resources Co. LtdHarbin150090China Guangdong Yuehai Water Investment Co. LtdShenzhen518021China UNSW Water Research Center School of Civil and Environmental EngineeringThe University of New South WalesSydneyNSW2032Australia

Chlorination has been intensively investigated for use in water disinfection and pollutant elimination due to its efficacy and convenience;however,the generation and transportation of chlorine and hypochlorite are energy-consuming and *** this study,a novel binary photosensitizer consisting of anthraquinone-2-sulfonate(AQ2S)and graphene was synthesized via a p-p stack adsorption method;this compound could allow for the chlorination of organic pollutants using on-site chlorine *** this photosensitive degradation process,sulfapyridine(SPY)was selected as a model pollutant and was decomposed by the reactive species(Cl2-,Cland O2-)generated during the photosensitive oxidation of *** synthesized AQ2S/graphene exhibited superior activity,and the degradation rate of SPY was over 90%after 12 h of visible light irradiation with a kinetic constant of 0.2034h*** show that 20 mg AQ2S/GR at a 21%weight percentage of AQ2S in a pH 7 SPY solution with 1 mol/L Clachieved the highest kinetics rate at 0.353 h*** radical trapping experiments demonstrated that Cl2-and O2-were the dominant species involved in SPY decomposition under solar *** reusability and stability of this composite were verified by conducting a cycle experiment over five successive *** capacity of photodegradation still remained over 90%after these 5 *** current study provides an energyefficient and simple-operational approach for water phase SPY control.

关键词： Photosensitizer AQ2S Visible-light-driven Free radicals trapping Reusability

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How to Promote Sales: Discount Promotion or Coupon Promotion?

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Journal of Systems science and Systems Engineering 2020年第4期29卷 381-399页

作者： Peng Wiang Rong Du Qiying Hu School of Economics and Management Xidian UniversityXi'an 710126China School of Management Fudan UniversityShanghai 200433China

In this paper,we examine how a merchant should choose between discount promotion(offering a discount through an online third-party promotion platform)and coupon promotion(ssuing on-package coupons directly to consumers).We develop a two-period model in which the merchant optimizes the promotion decision in the first period and does not promote in the second *** identify two consumer segments:informed consumers who are aware of the merchant's offering at the beginning of the first period and know the true quality of the product,and uninformed consumers who are not aware of the merchant's offering at the beginning of the first period and underestimate the product ***,the merchant has access only to informed consumers when adopting coupon promotion or when choosing not to promote,while the merchant can access both informed consumers and uninformed consumers when offering discount *** this setting,we find that the merchant should offer discount promotion when the quality estimation of uninformed consumers is large and/or when the proportion of informed consumers is small;otherwise,the merchant should adopt coupon promotion when the effect of coupons in the first period is large and choose not to promote when the effect of coupons in the first period is small.

关键词： Sales promotions on-package coupons coupon promotion discount promotion delayed in-centive

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