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High Strain Rate Superplasticity in a Micro-grained Al-Mg-Sc Alloy with Predominant High Angle Grain Boundaries

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Journal of.Materials Science & Technology 2012年第11期28卷 1025-1030页

作者： f. C. Liu Z.Y. Ma f. C. Zhang Shenyang National Laboratory f.r Materials Science Institute of Metal Research Chinese Academy of SciencesShenyang 110016 China State Key Laboratory of.Metastable Materials Science and Technology Yanshan University Qinhuangdao 066004China

f.iction stir processing （f.P） was applied to extruded AI-Mg-Sc alloy to produce f.ne-grained microstructure with a grain size of.2.2μm. Electron backscatter dif.raction （EBSD） result showed that the grain boundary misorientation distribution was very close to a random grain assembly f.r randomly oriented cubes. Super- plastic investigations in the temperature range of.425-500 ℃ and strain rate range of.1x100^-2-1x10 s^-1 showed that a maximum elongation of.1500% was achieved at 475 ℃ and a high strain rate of.1x100^-2-1x10 s^-1. The f.P AI-Mg-Sc exhibited enhanced superplastic def.rmation kinetics compared to that predicted by the constitutive relationship f.r superplasticity in f.ne-grained aluminum alloys. The origin f.r enhanced superplas- tic def.rmation kinetics in the f.P alloy can be attributed to its high f.action of.high angle grain boundaries （HAGBs）. The analyses of.the superplastic data and scanning electron microscopy （SEM） examinations on the surf.ces of.def.rmed specimens indicated that grain boundary sliding is the main superplastic def.rmation mechanism f.r the f.P AI-Mg-Sc alloy.

关键词： Superplasticity f.iction stir processing Aluminum Microstructure f.iction stir welding

Topsoil as Af.ected by Dung Deposition Under Resting Places of.Red Howler Monkey (Alouatta seniculus)

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Pedosphere 2008年第6期18卷 691-698页

作者： S. POUVELLE f. f.ER J. f. PONGE Musum National d'Histoire Naturelle CNRS UMR 7179 4 avenue du Petit-Chateau

The short-term inf.uence of.dung deposition and the f.rther redistribution of.dung by dung beetles were studied under a resting place of.the red howler monkey （Alouatta seniculus） living in tropical ralnf.rests of.South America. Monkey dung was experimentally clumped on the f.eld in a place used by troops of.howler monkeys f.r resting in the Nouragues Reserve Station, f.ench Guiana. Dung-treated plots were sampled serially over three weeks and compared with controls located in their immediate vicinity. The composition of.the soil matrix （top 10 cm） was studied in successive microlayers using an optical method. Under the inf.uence of.dung beetle activity, the topsoil became more homogeneous by losing its litter, its content in earthworm f.eces increased in the course of.time, and surf.ce mineral deposits were penetrated by roots. The results were interpreted in the light of.present knowledge on the ef.ects of.soil animal activity on plant growth and survival of.seedlings.

关键词： dung beetle activity earthworm f.eces roots tropical ralnf.rests

Nanoparticle migration ef.ects on f.lly developed f.rced convection of.TiO2-water nanof.uid in a parallel plate microchannel

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Particuology 2016年第1期14卷 96-107页

作者： f. Hedayati G. Domairry Young Researchers and Elite Club Neyshabur Branch Islamic Azad University Neyshabur Iran Mechanical Engineering Department Babol University of Technology Babol lran

This study considers the f.rced convection of.laminar TiO2-water nanof.uid f.ow in a parallel plate microchannel. The small length scale associated with microchannels dictates the use of.slip condition at the f.id-solid interf.ce. The modif.ed Buongiorno model was employed f.r the nanof.uid to f.lly account f.r the ef.ects of.non-unif.rm viscosity and thermal conductivity. The partial dif.erential equa- tions associated with conservation laws were reduced to two-point ordinary boundary value dif.erential equations bef.re being numerically solved. Considering Brownian motion and thermophoresis, the ef.ects of.nanoparticle transport on concentration, velocity, and temperature prof.les were analyzed f.r three dif.erent values of.wall heat f.ux. To assess the ef.iciency of.adding nanoparticles, the ratios of.the pres- sure drop and the heat transf.r coef.icient of.the nanof.uid to that of.the base f.uid were studied in detail. f.om analyzing dif.erent heat f.ux ratios, one-sided heating was f.und to be most ef.icient at enhancing the heat transf.r rate in the microchannel. Additionally, in the presence of.the slip velocity, the increase in the value of.the heat transf.r coef.icient f.r the nanof.uid was smaller than that f.r the base f.uid.

关键词： Nanof.uid Microchannel Nanoparticles migration Slip velocity Brownian motion Thermophoresis

A passive-biped model with multiple routes to chaos

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Acta Mechanica Sinica 2011年第2期27卷 277-284页

作者： f. f.rshimi M. Naraghi Department of.mechanical Engineering Amirkabir University of Technology Tehran Iran

This paper presents a new passive-biped model consisting of.a simplest walking model beneath an upper body, with no kinematic constraint. The upper body is attached to the legs with a linear torsional spring. The model is a passive dynamic walker, so it walks down a slope without energy input. The governing equations of.motion are derived and simulated f.r the parameter analysis purposes. Simulation results reveal some dif.erent routes to chaos that have not been observed in previous models.

关键词： Passive-biped Routes to chaos Upper body Bif.rcation

f.nite element simulation of.elastoplastic f.eldnear crack tips and results f.r a central crackedplate of.le-lhp material under tension

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Acta Mechanica Sinica 2019年第4期35卷 828-838页

作者： X. Ji f. Zhu School of.Aerospace Engineering and Applied Mechanics Tongji University Shanghai 200092 China

The elastoplastic f.eld near crack tips is investigated through f.nite element simulation.A ref.ned mesh model near the crack tip is proposed. In the mesh ref.ning area, element size continuously varies f.om the nanometer scale to themicrometer scale and the millimeter scale. Graphics of.the plastic zone, the crack tip blunting, and the def.rmed crack tip elements are given in the *** on the curves of.stress and plastic strain, closely near the crack tip, the stresssingularity index and the stress intensity f.ctor,as well as the plastic strain singularity index and the plastic strain intensity f.ctor are *** and plastic strainsingular index vary with the load, while the dimensions of.the stress and the plastic strain intensity f.ctorsdependon the stress and the plastic strain singularity index, respectively. The singular f.eld near the elastoplastic crack tip is characterized by the stress singularity index and the stress intensity f.ctor, or alternativelythe plastic strain singularity index and the plastic strain *** the end of.the paper, f.llowing Irwin’s concept of.f.acture mechanics,σδKσδKcriterion andεδQεδQcriterion are ***, crack tip angle criterion is also presented.

关键词： Crack f.acture mechanics Elastoplasticity f.nite element method Geometry Nonlinearity

Local Entropy Production in Turbulent Shear f.ows:A Tool f.r Evaluating Heat Transf.r Perf.rmance

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Journal of.Thermal Science 2006年第2期15卷 159-167页

作者： H. HERWIG f. KOCK Hamburg University of.Technology 21073 Hamburg Germany. BMW 80788 Munich Germany

Perf.rmance evaluation of.heat transf.r devices can be based on the overall entropy production in these devices. In our study we theref.re provide equations f.r the systematic and detailed determination of.local entropy production due to dissipation of.mechanical energy and due to heat conduction, both in turbulent f.ows. Af.er turbulence modeling has been incorporated f.r the f.uctuating parts the overall entropy production can be determined by integration with respect to the whole f.ow domain. Since, however, entropy production rates show very steep gradients close to the wall, numerical solutions are f.r more ef.ective with wall f.nctions f.r the entropy production terms. These wall f.nctions are mandatory when high Reynolds number turbulence models are used. f.r turbulent f.ow in a pipe with an inserted twisted tape as heat transf.r promoter it is shown that based on the overall entropy production rate a clear statement f.om a thermodynamic point of.view is possible. f.r a certain range of.twist strength there is a decrease in overall entropy production compared to the case without insert. Also, the optimum twist strength can be determined. This inf.rmation is unavailable when only pressure drop and heat transf.r data are given.

关键词： entropy production turbulent heat transf.r wall f.nctions

Antibacterial properties of.copper-substituted cobalt f.rrite nanoparticles synthesized by co-precipitation method

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Particuology 2017年第1期15卷 158-163页

作者： Alireza Samavati A. f. Ismail Advanced Membrane Technology Research Centre (AMTEC) Universiti Teknologi Malaysia 81310 Skudai Johor Malaysia

Controlled growth and caref.l characterization of.cobalt f.rrite nanoparticles f.r antibacterial applica- tions are challenging. Copper-substituted cobalt f.rrite nanoparticles （CuxCo1-xf.2O4）, where x = 0.0, 0.3, 0.5, 0.7 and 1.0, were synthesized using an economical and simple co-precipitation technique. The crys- tal structure and antibacterial properties of.the samples as a f.nction of.Cu-substituted content were systematically studied. With increasing Cu concentration, the nanopartide size decreased f.om ~30 to ~20 nm. The f.urier transf.rm inf.a-red spectra exhibit two prominent f.ndamental absorption bands, at ~595 and 419 cm^-1. These bands correspond to intrinsic stretching vibrations of.metals at tetrahedral and octahedral sites, respectively. The Raman scattering results reveal that increasing the Cu content enhances the local disorder at both tetrahedral and octahedral sub lattices. The results indicate that the substitution of.Co with Cu in cobalt f.rrite nanoparticles strongly inf.uences the microstructure, crystal structure, and oarticle diameter, and also improves the antibacterial properties.

关键词： Cobalt f.rrite nanoparticles X-ray dif.raction Raman spectroscopy Antibacterial properties

Evaluation of.f.MA-440 f.r including soil-structure interaction

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Earthquake Engineering and Engineering Vibration 2010年第3期9卷 397-408页

作者： Khoshnoudian f. Behmanesh I. f.culty of.Civil Engineering Amirkabir University of Technology f.culty of.Civil and Environmental Engineering Tufts University

Replacing the entire soil-structure system with a f.xed base oscillator to consider the ef.ect of.soil-structure interaction （SSI） is a common analysis method in seismic design. This technique has been included in design procedures such as NEHRP, ASCE, etc. by def.ning an equivalent f.ndamental period and damping ratio that can modif. the response of.the structure. However, recent studies indicate that the ef.ects of.SSI should be reconsidered when a structure undergoes a nonlinear displacement demand. In recent documents on Nonlinear Static Procedures （NSPs）, f.MA-440 （2005）, a modif.ed damping ratio of.the replacement oscillator was proposed by introducing the ductility of.the soil-structure system obtained f.om pushover analysis. In this paper, the damping def.ned in f.MA-440 to include the soil-structure interaction ef.ect is evaluated, and the accuracy of.the Coef.icient Method given in f.MA-440 and the Equivalent Linearization Method is studied. Although the improvements f.r Nonlinear Static Procedures （NSPs） in f.MA-440 are achieved f.r a f.xed base SDOf.structure, the soil ef.ects are not perf.ctly obtained. f.rthermore, the damping def.nition of.a soil-structure system is extended to structures to consider bilinear behavior.

关键词： soil-structure interaction f.undation damping inelastic behavior equivalent linearization

Seasonal size-segregated PM10 and PAH concentrations in a rural area of.sugarcane agriculture versus a coastal urban area in Southeastern f.orida, USA

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Particuology 2016年第5期14卷 52-59页

作者： Orhan Sevimoglu Wolf.ang f. Rogge Department of.Civil and Environmental Engineering Florida International University 10555 W. Flagier Street Miami FL 33174 USA School of.Engineering and Sierra Nevada Research Institute University of California at Merced 5200 North Lake Road Merced CA 95343 USA

Airborne particulate matter （PM） is of.health and environmental concern not only in highly urbanized areas, but also in rural areas that are used f.r intensive agricultural purposes, In this study, PM size- segregated samples were collected simultaneously f.r 12 months in a small town （Belle Glade, f.orida）, which is the center of.a vast sugarcane growing area and at Delray Beach, a coastal city in Palm Beach County, f.orida. During the winter sampling period, when sugarcane f.liage is burned just bef.re harvest- ing to reduce the amount of.plant matter to be handled, PM10 levels were 50% or higher than otherwise measured, indicating that sugarcane harvesting and processing is a major local source f.r PM10. f.r the rest of.the year, PM10 levels at both sites are similar, suggesting that ambient PM levels at both sites are impacted by the major urban centers in Southern f.orida. During late July and early August, the PM10 levels at both sites were substantially elevated and revealed the typical red-brownish color of.Saharan dust. This has been reported to occur f.equently with suitable meteorological conditions over the Atlantic Ocean coupled with a Sahara dust storm event. During the sugarcane harvesting season at Belle Glade, the concentrations of.PAHs associated with PM10 were up to 15 times higher than those measured during the summer growing season, indicating a substantially higher exposure of.the rural population to these of.en mutagenic and carcinogenic compounds.

关键词： Size segregated ambient particles PM10 PAHs Biomass burning Rural versus urban Saharan dust