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Instability of single-walled carbon nanotubes conveying Jeffrey fluid

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Chinese Physics B 2021年第4期30卷 328-332页

作者： Bei-nan jia Yong-Jun jian School of Mathematical Science Inner Mongolia UniversityHohhot 010021China

We report instability of the single-walled carbon nanotubes(SWCNT) filled with non-Newtonian Jeffrey *** objective is to get the influences of relaxation time and retardation time of the Jeffrey fluid on the vibration frequency and the decaying rate of the amplitude of carbon *** elastic Euler-Bernoulli beam model is used to describe vibrations and structural instability of the carbon nanotubes.A new vibration equation of an SWCNT conveying Jeffrey fluid is first derived by employing Euler-Bernoulli beam equation and Cauchy momentum equation taking constitutive relation of Jeffrey fluid into *** complex vibrating frequencies of the SWCNT are computed by solving a cubic eigenvalue problem based upon differential quadrature method(DQM).It is interesting to find from computational results that retardation time has significant influences on the vibration frequency and the decaying rate of the ***,the vibration frequency decreases and critical velocity increases with the retardation *** is to say,longer retardation time makes the SWCNT more stable.

关键词： single-walled carbon nanotubes Jeffrey fluid relaxation time retardation time

Dependence of Estimating Whitecap Coverage on Currents and Swells

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Journal of Ocean University of China 2021年第3期20卷 512-520页

作者： LIU Min YANG Bailin jia nan ZOU Zhongshui Ocean College Hebei Agriculture UniversityQinhuangdao 066000China School of Resources and Materials Northeastern University at QinhuangdaoQinhuangdao 066004China PLA Information Engineering University Zhengzhou 450001China School of Marine Science Sun Yat-Sen UniversityZhuhai 519082China

The shipboard measurements of whitecap coverage(W)and the meteorological and oceanographic information from two cruises in the South China Sea and Western Pacific are explored for estimating *** study aims at evaluating how to im-prove the parameterizations of W while considering the effects of currents and swells on wave *** indeed affect W in a way that winds with following currents can decrease W,whereas winds with opposing currents can increase ***,10-m wind speed over sea surface(U_(10))is calibrated by subtracting the current velocity from U_(10) when the propagating directions of winds and currents are *** contrast,when the direction is opposite,U_(10) is calibrated by adding the parallel velocity com-ponent of the opposing current to U_(10).The power fits of W dependence on the U_(10)-related parameters of U_(10),friction velocity,wind sea Reynolds number in terms of this calibrated-U_(10) obtain better results than those directly fitted to U_(10).Different from the effect of currents on W,wind blowing along the crest line of swells may contribute to the increase in *** conclusions suggest that U_(10) should be calibrated first before parameterizing W in areas with a strong current or some swell-dominant areas.

关键词： whitecap coverage currents friction velocity wind sea Reynolds number swells

Neutron Diffraction Study of Low-Cycle Fatigue Behavior in an Austenitic–Ferritic Stainless Steel

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Acta Metallurgica Sinica(English Letters) 2015年第10期28卷 1247-1256页

作者： Ming-Wei Zhu nan jia Feng Shi Bjorn Clausen School of Materials Science and Engineering Shenyang Aerospace University Key Laboratory for Anisotropy and Texture of Materials(ATM) Northeastern University School of Science Northeastern University Los Alamos National Laboratory Los Alamos Neutron Science Center

By performing in situ neutron diffraction experiments on an austenitic-ferritic stainless steel subjected to lowcycle fatigue loading, the deformation heterogeneity of the material at microscopic level has been revealed. Based on the in situ neutron diffraction data collected from a single specimen together with the mechanical properties learned from the ex situ micro-hardness, a correlation has been found. The performance versus diffraction-profile correlation agrees with the cyclic-deformation-induced dislocation evolution characterized by ex situ TEM observation. Moreover, based on the refined neutron diffraction-profile data, evident strain anisotropy is found in the austenite. The high anisotropy in this phase is induced by the increase in dislocation density and hence contributes to the hardening of the steel at the first 10 *** 10 fatigue cycles, the annihilation and the rearrangement of the dislocations in both austenitic and ferritic phases softens the plastically deformed specimen. The study suggests that the evolution of strain anisotropy among the differently oriented grains and micro-strain induced by lattice distortion in the respective phases mostly affect the cyclic-deformationinduced mechanical behavior of the steel at different stages of fatigue cycles. The stress discrepancy between phases is not the dominant mechanism for the deformation of the steel.

关键词： Duplex steel Neutron diffraction Fatigue Plastic deformation Microstructure

Orientation-Dependent Mechanical Responses and Plastic Deformation Mechanisms of FeMnCoCrNi High-entropy Alloy:A Molecular Dynamics Study

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Acta Metallurgica Sinica(English Letters) 2021年第11期34卷 1511-1526页

作者： Hai-Feng Zhang Hai-Le Yan Feng Fang nan jia Key Laboratory for Anisotropy and Texture of Materials(Ministry of Education) School of Material Science and EngineeringNortheastern UniversityShenyang 110819China State Key Lab Rolling&Automat Northeastern UniversityShenyang 110819China

Mechanical properties of high-entropy alloys(HEAs)with the face-centered cubic(fcc)structure strongly depend on their initial grain ***,the orientation-dependent mechanical responses and the underlying plastic fl ow mechanisms of such alloys are not yet well ***,deformation of the equiatomic FeMnCoCrNi HEA with various initial orientations under uniaxial tensile testing has been studied by using atomistic simulations,showing the results consistent with the recent experiments on fcc *** quantitative analysis of the activated deformation modes shows that the initiation of stacking faults is the main plastic deformation mechanism for the crystals initially oriented with[001],[111],and[112],and the total dislocation densities in these crystals are higher than that with the[110]and[123]*** faults,twinning,and hcp-martensitic transformation jointly promote the plastic deformation of the[110]orientation,and twinning in this crystal is more significant than that with other *** in the crystal oriented with[123]is dominated by the hcp-martensite *** of the mechanical behaviors in the FeMnCoCrNi alloy and the conventional materials,*** and Fe50Ni50,has shown that dislocation slip tends to be activated more readily in the *** is attributed to the larger lattice distortion in the HEA than the low-entropy materials,leading to the lower critical stress for dislocation nucleation and elastic–plastic transition in the *** addition,the FeMnCoCrNi HEA with the larger lattice distortion leads to an enhanced capacity of storing ***,for the[001]-oriented HEA in which dislocation slip and stacking fault are the dominant deformation mechanisms,the limited deformation modes activated are insu fficient to improve the work hardening ability of the material.

关键词： High-entropy alloy Molecular dynamics study Mechanical response Plastic deformation mechanism

Abnormal chemical composition fluctuations in multi-principal-element alloys induced by simple cyclic deformation

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Journal of Materials Science & Technology 2022年第18期113卷 287-295页

作者： Mengyuan He nan jia Xiaochun Liu Yongfeng Shen Liang Zuo Key Laboratory for Anisotropy and Texture of Materials(Ministry of Education) School of Materials Science and EngineeringNortheastern UniversityShenyang 110819China Institute of Metals College of Materials Science and EngineeringChangsha University Of Science and TechnologyChangsha 410114China

High entropy alloys exhibit excellent combination of mechanical properties because of the unique com-position fluctuations,termed as‘concentration wave’.The concentration wave was closely related to mul-tiple aspects,including the fluctuation of local strain energy,local atomic environment,electronegativity,*** we report for the first time that the amplitude of the concentration wave can be mechani-cally tailored under cyclic deformation in a well-known Cantor ***-scale energy-dispersive X-ray spectroscopy(EDS)mapping reveals that cyclic deformation may dynamically induce the clustering of solute atoms with a size of 1-3 nm,thus resulting in a higher concentration wave *** con-centration wave promotes strong interactions between dislocations and local solute *** from the typical Taylor strengthening contribution due to the presence of isolated dislocations,the strength enhancement from the mechanically induced composition fluctuations was quantified to be as high as∼70 MPa,about one-third of the yield strength of the alloy without *** opens up a novel strategy of designing high strength alloys by tailoring solute configurations.

关键词： Cantor alloy Cyclic deformation Concentration wave EDS maps

Synergy effect of multi-strengthening mechanisms in FeMnCoCrN HEA at cryogenic temperature

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Journal of Materials Science & Technology 2021年第27期86卷 158-170页

作者： Zhufeng He nan jia Hongwei Wang Haile Yan Yongfeng Shen Key Laboratory for Anisotropy and Texture of Materials(Ministry of Education) School of Material Science and EngineeringNortheastern UniversityShenyang 110819China State Key Lab Rolling&Automat Northeastern UniversityShenyang 110819China

High-entropy alloys(HEAs)have attracted great research interest owing to their good combination of high strength and ductility at both room and cryogenic ***,expensive raw materials are always added to overcome the strength-ductility trade-off at low temperatures,leading to an increased production cost for the cryogenically used *** this work,a series of nitrogen-doped Fe Mn Co Cr HEAs have been processed by homogenization annealing,cold rolling and recrystallization annealing followed by water *** microstructural evolution and mechanical properties of the alloys are studied *** Fe_(49)Mn_(30)Co_(10)Cr_(10)N1alloy shows excellent mechanical properties at both 293 K and 77 ***,the yield and ultimate tensile strength of 1078 and 1630 MPa are achieved at the cryogenic temperature,respectively,while a satisfactory uniform elongation of 33.5%is *** ultrahigh yield strength results from the microstructure refinement caused by the activation of athermal martensitic transformation and mechanical twinning that occur in the elastic regime together with the increased lattice friction due to the cryogenic *** the plastic regime,the dynamic Hall-Petch effect caused by twinning,martensitic transformation,and reverse transformation together with the high barrier to dislocation motion jointly contribute to the ultrahigh tensile ***,the transformation induced plasticity(TRIP)and the twinning induced plasticity(TWIP)effects jointly contribute to the *** design strategy for attaining superior mechanical properties at low temperatures,*** adjusting stacking fault energy in the interstitial metastable HEAs,guides the development of high-performance and low-cost alloys for cryogenic applications.

关键词： High-entropy alloy Cryogenic deformation Nitrogen doping Phase transformation Twinning

Reverse Transformation in[110]-Oriented Face-Centered-Cubic Single Crystals Studied by Atomic Simulations

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Acta Metallurgica Sinica(English Letters) 2022年第10期35卷 1631-1640页

作者： Hai-Feng Zhang Hai-Le Yan Feng Fang nan jia Key Laboratory for Anisotropy and Texture of Materials(Ministry of Education) School of Material Science and EngineeringNortheastern UniversityShenyang110819China State Key Lab Rolling&Automat Northeastern UniversityShenyang110819China

Bidirectional transformations,which are achieved by triggering both dynamic forward transformation from the face-centered-cubic(fcc)austenite to the hexagonal-close-packed(hcp)martensite and the reverse transformation from martensite to austenite during cold deformation,have been previously reported in FeMnCoCr-based high-entropy alloys(HEAs).This leads to the permanent refinement of microstructure and hence enhances the work-hardening capacity of *** order to reveal the microscopic mechanism of the reverse transformation in HEAs under deformation,the effect of the sample aspect ratio,i.e.,Z/X,on the evolution of deformation systems in the equi-atomic FeMnCoCrNi alloy with[110]orientation during uniaxial tensile loading along the Z direction is investigated by atomic simulations in this *** the aspect ratio is 0.5,the reverse transformation is more significant compared with other models,while a good plasticity can still be *** then compare the micromechanical behavior of three fcc single crystals,i.e.,FeMnCoCrNi,FeCuCoCrNi,and pure *** results show that the stacking fault energy plays a major role in the activation of different deformation mechanisms;however,the lattice distortion in the HEA does not significantly affect the activation of deformation ***,for all materials dislocation slip leads to the softening,while strain hardening is attributed to the initiation of multiple deformation *** Shockley partials slip leads to bidirectional phase transition,twinning and detwinning in the three ***,the reverse transformation can occur in all metallic materials where the fcc to hcp phase transformation is the dominant deformation *** findings contribute to an in-depth understanding of the deformation mechanism in fcc-structured materials under severe plastic deformation and provide theoretical guidance for the design of alloys with superior strength–plasticity combinations.

关键词： Face-centered-cubic materials Atomic simulation Plastic deformation Reverse transformation

Towards privacy-preserving and efficient word vector learning for lightweight IoT devices

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Digital Communications and Networks 2024年第4期10卷 895-903页

作者： nan jia Shaojing Fu Guangquan Xu Kai Huang Ming Xu National University of Defense Technology ChangshaChina Big Data School Qingdao Huanghai UniversityQingdaoChina Tianjin Key Laboratory of Advanced Networking College of Intelligence and ComputingTianjin UniversityTianjinChina College of Joint Operations National Defense UniversityShijiazhuangChina

Nowadays,Internet of Things(IoT)is widely deployed and brings great opportunities to change people's daily *** realize more effective human-computer interaction in the IoT applications,the Question Answering(QA)systems implanted in the IoT services are supposed to improve the ability to understand natural ***,the distributed representation of words,which contains more semantic or syntactic information,has been playing a more and more important role in the QA ***,learning high-quality distributed word vectors requires lots of storage and computing resources,hence it cannot be deployed on the resource-constrained IoT *** is a good choice to outsource the data and computation to the cloud ***,it could cause privacy risks to directly upload private data to the untrusted ***,realizing the word vector learning process over untrusted cloud servers without privacy leakage is an urgent and challenging *** this paper,we present a novel efficient word vector learning scheme over encrypted *** first design a series of arithmetic computation *** we use two non-colluding cloud servers to implement high-quality word vectors learning over encrypted *** proposed scheme allows us to perform training word vectors on the remote cloud servers while protecting *** analysis and experiments over real data sets demonstrate that our scheme is more secure and efficient than existing privacy-preserving word vector learning schemes.

关键词： Privacy-preserving Word vector learning Secret sharing Internet of things

Multi-Source Characteristics of Atmospheric Deposition in nanjing,China,as Controlled by East Asia Monsoons and Urban Activities

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Pedosphere 2016年第3期26卷 374-385页

作者： LI Shanquan ZHANG Ganlin YANG Jinling jia nan State Key Laboratory of Soil and Sustainable Agriculture Institute of Soil Science Chinese Academy of Sciences Nanjing 210008 (China) University of Chinese Academy of Sciences Beijing 100049 (China)

Atmospheric deposition, a major pathway of metals entering into soils, plays an important role in soil environment, especially in urban regions where a large amount of pollutants are emitted into atmosphere through various sources. In order to understand the characteristics of atmospheric deposition in urban area and its relation with natural and anthropogenic sources, a three-year study of atmospheric deposition at three typical sites, industrial zone(IN), urban residential area(RZ) and suburban forested scenic area(FA),was carried out in nanjing, a metropolitan city in eastern China from 2005 to 2007. The bulk deposition rate and element composition of atmospheric deposition varied spatio-temporally in the urban zones of nanjing. The concentrations of Cu, Zn, Pb and Ca in the atmospheric deposits were strongly enriched in the whole nanjing region; however, anthropogenic pollutants in atmospheric deposits were diluted by the input of external mineral dust transported from northwestern China. Source apportionment through principal component analysis(PCA) showed that the background atmospheric deposition at the FA site was the combination of external aerosol and local emission sources. The input of long-range transported Asian dust had an important influence on the urban background deposition, especially in spring when the continental dust from the northwestern China prevailed. Marine aerosol source was observed in summer and autumn, the seasons dominated by summer monsoon in nanjing. In contrast, the contribution of local anthropogenic emission source was constant regardless of seasons. At the RZ and IN sites, the atmospheric deposition was more significantly affected by the nearby human activities than at the FA site. In addition, different urban activities and both the winter and summer Asian monsoons had substantial impacts on the characteristics of dust deposition in urban nanjing.

关键词： aerosol anthropogenic pollutants Asian dust metals source apportionment urban environment