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Effect of electric boundary conditions on crack propagation in ferroelectric ceramics

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Acta Mechanica Sinica 2014年第2期30卷 153-160页

作者： f.-X. Li Y.Sun r.K.n.D.rajapakse State Key Laboratory for Turbulence and Complex Systems College of EngineeringPeking University faculty of Applied Sciences Simon Fraser University

In this paper, the effect of electric boundary conditions on Mode I crack propagation in ferroelectric ceramics is studied by using both linear and nonlinear piezoelectric fracture mechanics. In linear analysis, impermeable cracks under open circuit and short circuit are analyzed using the Stroh formalism and a rescaling method. It is shown that the energy release rate in short circuit is larger than that in open circuit. In nonlinear analysis, permeable crack conditions are used and the nonlinear effect of domain switching near a crack tip is considered using an energy-based switching criterion proposed by Hwang et al.（Acta Metal. Mater.,1995）. In open circuit, a large depolarization field induced by domain switching makes switching much more diffcult than that in short circuit. Analysis shows that the energy release rate in short circuit is still larger than that in open circuit, and is also larger than the linear result. Consequently,whether using linear or nonlinear fracture analysis, a crack is found easier to propagate in short circuit than in open circuit, which is consistent with the experimental observations of Kounga njiwa et al.（Eng. fract. Mech., 2006）.

关键词： ferroelectric ceramics Crack propagation En-ergy release rate Electric boundary conditions Domain switching

Synthesis and Electrical Properties of Well-Ordered Layered α-MoO_3 nanosheets

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nano-Micro Letters 2011年第4期3卷 242-248页

作者： r.naouel H.Dhaouadi f.Touati n.Gharbi Laboratoire de Chimie de la Matière Condensée Université de Tunis.Institut Préparatoire aux Etudes d’Ingénieur de Tunis "Laboratoire des Matériaux Utiles" Institut national de recherche et d’Analyse Physico-chimique

α-MoO_3 ordered nanosheets have been synthesized under hydrothermal conditions using commercial MoO_3 and hydroquinone as structuring agent. X-ray diffraction(XrD), scanning electron microscope(SEM) and transmission electron microscopy(TEM) were used to analyse the obtained material. The conductivity mechanism of the Molybdenum ordered nanosheets has been investigated using combined complex impedance and modulus *** temperature dependence of the conductivity, which was between 473 and 573 K, is very close to the Arrhenius' law, with an activation energy of 0.76 eV. However, the conductivity of the material increases with temperature. It shows a typical negative temperature coefficient resistance(nTCr) similar to that of a semiconductor. The dielectric properties of the MoO_3 compound have been studied in the temperature range of 473-573 K as well as the frequency range of 10 Hz to 13 MHz. The ac-conductivity for high frequency σac(ω)obeys the universal power law.

关键词： Electron microscopy Hydrothermal synthesis X-ray diffraction Electrical properties

replication of natural surface topographies to generate advanced cell culture substrates

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Bioactive Materials 2023年第10期28卷 337-347页

作者： n.O.Monteiro J.f.fangueiro r.L.reis n.M.neves 3B’s research Group I3Bs-Research Institute on BiomaterialsBiodegradables and BiomimeticsUniversity of MinhoHeadquarters of the European Institute of Excellence on Tissue Engineering and Regenerative MedicineAveParkParque de Ciencia e Tecnologi1Zona Industrial da Gandr14805-017BarcoGuimaraesPortugal ICVS/3B’s-PT Government Associate Laboratory Brag1Guimar˜aesPortugal

Surface topographies of cell culture substrates can be used to generate in vitro cell culture environments similar to the in vivo cell niches. In vivo, the physical properties of the extracellular matrix (ECM), such as its topography, provide physical cues that play an important role in modulating cell function. Mimicking these properties remains a challenge to provide in vitro realistic environments for cells. Artificially generated substrates’ topographies were used extensively to explore this important surface cue. More recently, the replication of natural surface topographies has been enabling to exploration of characteristics such as hierarchy and size scales relevant for cells as advanced biomimetic substrates. These substrates offer more realistic and mimetic environments regarding the topographies found in vivo. This review will highlight the use of natural surface topographies as a template to generate substrates for in-vitro cell culture. This review starts with an analysis of the main cell functions that can be regulated by the substrate’s surface topography through cell-substrate interactions. Then, we will discuss research works wherein substrates for cell biology decorated with natural surface topographies were used and investigated regarding their influence on cellular performance. At the end of this review, we will highlight the advantages and challenges of the use of natural surface topographies as a template for the generation of advanced substrates for cell culture.

关键词： Biomimetic topography Cell culture substrates natural surface topographies

Exploring nationally and regionally defined models for large area population mapping

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International Journal of Digital Earth 2015年第12期8卷 989-1006页

作者： A.E.Gaughan f.r.Stevens C.Linard n.n.Patel A.J.Tatem Department of Geography and Geosciences University of LouisvilleLouisvilleKYUSA Biological Control and Spatial Ecology UniversitéLibre de BruxellesBrusselsBelgium Department of Geography and Geoinformation Science George Mason UniversityFairfaxVAUSA Department of Geography and Environment University of SouthamptonSouthamptonUK fogarty International Center National Institutes of HealthBethesdaMDUSA flowminder foundation StockholmSweden

Interactions between humans,diseases,and the environment take place across a range of temporal and spatial scales,making accurate,contemporary data on human population distributions critical for a variety of *** for disaggregating census data to finer-scale,gridded population density estimates continue to be refined as computational power increases and more detailed census,input,and validation datasets become ***,the availability of spatially detailed census data still varies widely by *** this study,we develop quantitative guidelines for choosing regionally-parameterized census count disaggregation models over country-specific *** examine underlying methodological considerations for improving gridded population datasets for countries with coarser scale census data by investigating regional versus country-specific models used to estimate density surfaces for redistributing census *** is given to the spatial resolution of input census data using examples from East Africa and Southeast *** suggest that for many countries more accurate population maps can be produced by using regionally-parameterized models where more spatially refined data exists than that which is available for the focal *** study highlights the advancement of statistical toolsets and considerations for underlying data used in generating widely used gridded population data.

关键词： human population modeling random forest regression dasymetric mapping gridded population datasets

Application of particle splitting method for both hydrostatic and hydrodynamic cases in SPH

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Acta Mechanica Sinica 2018年第4期34卷 601-613页

作者： W.T.Liu P.n.Sun f.r.Ming A.M.Zhang College of Shipbuilding Engineering Harbin Engineering University

Smoothed particle hydrodynamics（SPH） method with numerical diffusive terms shows satisfactory stability and accuracy in some violent fluid–solid interaction problems. However, in most simulations, uniform particle distributions are used and the multi-resolution, which can obviously improve the local accuracy and the overall computational efficiency, has seldom been applied. In this paper, a dynamic particle splitting method is applied and it allows for the simulation of both hydrostatic and hydrodynamic problems. The splitting algorithm is that, when a coarse（mother） particle enters the splitting region, it will be split into four daughter particles, which inherit the physical parameters of the mother particle. In the particle splitting process,conservations of mass, momentum and energy are ensured. Based on the error analysis, the splitting technique is designed to allow the optimal accuracy at the interface between the coarse and refined particles and this is particularly important in the simulation of hydrostatic cases. finally, the scheme is validated by five basic cases, which demonstrate that the present SPH model with a particle splitting technique is of high accuracy and efficiency and is capable for the simulation of a wide range of hydrodynamic *** particle hydrodynamics（SPH）method with numerical diffusive terms shows satisfactory stability and accuracy in some violent fluid–solid interaction ***,in most simulations,uniform particle distributions are used and the multi-resolution,which can obviously improve the local accuracy and the overall computational efficiency,has seldom been *** this paper,a dynamic particle splitting method is applied and it allows for the simulation of both hydrostatic and hydrodynamic *** splitting algorithm is that,when a coarse（mother）particle enters the splitting region,it will be split into four daughter particles,which inherit the physical parameters of the mother *** the pa

关键词： Smoothed particle hydrodynamics Particle splitting Particle refinement Solid wall boundary fluid–structure interaction

Quantifying the Microstructures of Pure Cu Subjected to Dynamic Plastic Deformation at Cryogenic Temperature

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Journal of Materials Science & Technology 2011年第8期27卷 673-679页

作者： f. Yan H. W. Zhang n.r. Tao K. Lu Shenyang national Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China

A pure Cu （99.995 wt%） has been subjected to dynamic plastic deformation at cryogenic temperature to a strain of 2.1. Three types of microstructures that are related to dislocation slip, twinning and shear banding have been quantitatively characterized by transmission electron microscopy （TEM） assisted by convergent beam electron diffraction （CBED） analysis. Microstructures originated from dislocation slip inside or outside the shear bands are characterized by low angle boundaries （〈15°） that are spaced in the nanometer scale, whereas most deformation twins are deviated from the perfect ∑3 coincidence （60°/〈111〉） up to the maximum angle of 9°. The quantitative structural characteristics are compared with those in conventionally deformed Cu at low strain rates, and allowed a quantitative analysis of the flow stress-structural parameter relationship.

关键词： Quantitative structural characterization Cu Dynamic plastic deformation Trans mission electron microscopy Convergent beam electron diffraction

Power Quality Improvement of Distribution network Using BESS and Capacitor Bank

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Journal of Modern Power Systems and Clean Energy 2021年第3期9卷 625-632页

作者： f.r.Islam A.Lallu K.A.Mamun K.Prakash n.K.roy University of Sunshine Coast Sip-py DownsAustralia University of South Pacific SuvaFiji KJiulna University of Engineering and Technology KhulnaBangladesh

The power demand around the world is increasing *** aging distribution network architectures are used by the existing utility companies to deliver power to the consumers,which significantly affects the reliability,stability and quality of the delivered *** techniques such as compensation devices have been used by power system engineers and researchers to maintain the quality of power transmitted to end *** this paper,wattage and volt-amp reactive(VAr)planning scheme has been proposed by using the combination of battery energy storage systems(BESS)and compensators to deal with the vulnerability of networks to voltage drop and system *** cost-effective combination of BESS and shunt capacitor bank will then be analyzed to indicate the benefit of the proposed scheme.

关键词： Battery energy storage system(BESS) shunt capacitor bank reliability stability quality volt-amp reactive(VAr)planning distribution network

Carbon stocks in a highly fragmented landscape with seasonally dry tropical forest in the neotropics

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forest Ecosystems 2022年第2期9卷 168-177页

作者： n.Mesa-Sierra J.Laborde r.Chaplin-Kramer f.Escobar Instituto Tecnologico y de Estudios Superiores de Occidente Centro Interdisciplinario para la Formacion y Vinculacion SocialPeriferico Sur Manuel Gomez Morin 858545604TlaquepaqueJaliscoMexico Gnosis-naturaleza con ciencia A.C.Lorenzo Barcelata 510145239GuadalajaraJaliscoMexico Instituto de Ecologia A.C.Ecologia FuncionalCarretera Antigua a Coatepec 351El Haya91073XalapaVeracruzMexico natural Capital Project Woods Institute for the EnvironmentStanford University327 Campus DriveStanfordCA94305USA Institute on the Environment University of Minnesota1954 Buford AveSt.PaulMinnesota55108USA Instituto de Ecologia A.C.EcoetologiaCarretera Antigua a Coatepec 351El Haya91073XalapaVeracruzMexico

Background:Global modeling of carbon storage and sequestration often mischaracterizes unique ecosystems such as the seasonally dry tropical forest of the central region of the Gulf of Mexico,because species diversity is usually underestimated,as is their carbon *** this study,aboveground and soil carbon stocks were estimated to determine the climate mitigation potential of this highly degraded landscape(f forest cover).results:Tree species in the study area had carbon content values that were 30%–40%higher than the standard value proposed by the IPCC(i.e.,50%).Tropical oak forest in the region,despite its restricted distribution and low species richness,accounted for the highest mean carbon stocks per unit *** main factors driving spatial variability in carbon stocks were:maximum precipitation,soil organic matter,clay and silt *** strong relationship was found between aboveground carbon stocks and soil organic carbon in the study ***-fication of carbon stocks is an important consideration in the assessment of the conservation value of remnants of native vegetation in human-modified ***:This study demonstrates the importance of the highly fragmented tropical dry regions of the neo-tropics in maintaining landscape functionality and providing key ecosystem services such as carbon *** results also highlight how crucial field-based studies are for strengthening the accuracy of global ***,this approach reveals the real contribution of ecosystems that are not commonly taken into account in the mitigation of climate change effects.

关键词： Seasonally dry tropical region Ecosystem services Carbon sequestration Human modified landscapes Climate change mitigation

MHD stagnation-point flow and heat transfer towards stretching sheet with induced magnetic field

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Applied Mathematics and Mechanics(English Edition) 2011年第4期32卷 409-418页

作者： f.M.ALI r.nAZAr n.M.ArIfIn I.POP Department of Mathematics Institute of Mathematical ResearchUniversiti Putra Malaysia School of Mathematical Sciences Faculty of Science and TechnologyUniversiti Kebangsaan Malaysia faculty of Mathematics University of Cluj

The problem of the steady magnetohydrodynamic （MHD） stagnation-point flow of an incompressible viscous fluid over a stretching sheet is studied. The effect of an induced magnetic field is taken into account. The nonlinear partial differential equations are transformed into ordinary differential equations via the similarity transformation. The transformed boundary layer equations are solved numerically using the shooting method. numerical results are obtained for various magnetic parameters and Prandtl numbers. The effects of the induced magnetic field on the skin friction coefficient, the local nusselt number, the velocity, and the temperature profiles are presented graphically and discussed in detail.

关键词： boundary layer heat transfer induced magnetic field numerical solution magnetohydrodynamic (MHD) flow stretching sheet