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Effect of induced shielding current transmission in longitudinal direction on levitation force of melt grown single-domain YBa_2Cu_3O_(7-x) cylindrical superconductor

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Science China(Physics,Mechanics & Astronomy) 2004年第2期47卷 146-153页

作者： r. Nicolsky r. de Andrade Jr LASUP-DEE UFRJ Ilha do Fundao Cx.P.68515 21945-970 Rio de Janeiro RJ Brasil Correspondence should be addressed to Yang Wanmin LASUP-DEE UFRJ Ilha do Fundao Cx.P.68515 21945-970 Rio de Janeiro RJ Brasil Correspondence should be addressed to Yang Wanmin

A novel layer deletion method is used to experimentally investigate the effect of induced shielding current transmission (ISCT) in the longitudinal direction on the levitation force of a single-domain YBa2Cu3O7?x (YBCO) cylindrical superconductor (?30×7 mm). In the experiment the sample was gradually sliced into two equal sheets, at the middle height along a diameter with 5 mm every step. The experimental results show that the levitation force is closely related with the ISCT in the longitudinal direction. Any layer deletion, even a small piece of layer deletion can reduce the levitation force of the sample. After the whole layer was deleted the levitation force can diminish about 50%. It is also found that the levitation force is directly proportional to the effective factor of surface area, which is equal to the top surface area divided by the total surface area parallel to the top surface of the sample.

关键词： melt growth, single domain YBCO, levitation force, induced current distribution.

relating thermal conductivity of soil skeleton with soil texture by the concept of“local thermal conductivity fluctuation”

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Journal of rock Mechanics and Geotechnical Engineering 2022年第1期14卷 262-271页

作者： Adrian rózanski Faculty of Civil Engineering Wroclaw University of Science and TechnologyWybrzeze Wyspia_nskiego 2750-370WrocławPoland

The thermal conductivity of the soil skeletonλ;is an essential parameter from the point of view of the correct assessment of soil overall/effective *** work introduces the concept of“local thermal conductivity fluctuation”which characterizes the microscale variation of conductivity within the solid *** is proposed to link the“local fluctuation”of thermal conductivityλwith the soil texture-the information that is available at the scale of engineering *** was possible to relate the skeleton thermal conductivity with the grain size distribution of the ***,based on a large series of numerical simulations,the paper provides four triangle diagrams(at different organic matter contents:0%,2%,4%and 6%)relating the value ofλ;with volume fraction of individual soil *** result is extremely important from the practical point of *** can quickly evaluateλ;value provided that information on the grain size distribution and organic matter content is available.

关键词： Soil skeleton Probability density function(PDF) Computational micromechanics Local fluctuation Soil texture

Microstructural and mechanical properties of Al-4.5wt% Cu reinforced with alumina nanoparticles by stir casting method

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International Journal of Minerals,Metallurgy and Materials 2013年第10期20卷 978-985页

作者： N.Valibeygloo r.Azari Khosroshahi r.Taherzadeh Mousavian Faculty of Materials Engineering Sahand University of Technology Department of Metallurgy Zanjan BranchIslamic Azad University

The microstructure and mechanical properties of A1-4.5wt% Cu Mloy reinforced with different volume fractions （1.5vo1%, 3vo1%, and 5vo1%） of alumina nanoparticles, fabricated using stir casting method, were investigated. CMculated amounts of alumina nanoparticles （about ~50 nm in size） were ball-milled with aluminum powders in a planetary ball mill for 5 h, and then the packets of milled powders were incorporated into molten Al-4.5wt% Cu alloy. Microstructural studies of the nanocomposites reveal a uniform distribution of alumina nanoparticles in the A1-4.5wt% Cu matrix. The results indicate an outstanding improvement in compression strength and hardness due to the effect of nanoparticle addition. The aging behavior of the composite is also evaluated, indicating that the addition of alumina nanoparticles can accelerate the aging process of the Mloy, resulting in higher peak hardness values.

关键词： metallic matrix composites nanocomposites aluminum alumina nanoparticles casting mechanical proper-ties microstructure

Polymer Sensitized Quasi Solid-State Photovoltaic Cells Using Derivatives of Polythiophene

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Journal of Materials Science & Technology 2006年第6期22卷 811-816页

作者： G.K.r.Senadeera J.M.r.C.Fernando Institute of Fundamental Studies Hantane RoadKandySri Lanka Institute of Fundamental Studies Hantane RoadKandySri Lanka Postgraduate Institute of ScienceUniversity of PeradeniyaPeradeniyaSri Lanka

Substituted thiophene sensitized, nanocrystalline TiO2-based quasi solid-state solar cells were fabricated by using either poly （3-thiophene acetic acid）（P3TAA） or a copolymer with poly （3-thiophene acetic acid）-poly （hexyl thiophene）（P3TAA-PHT） polymers and copper iodide （Cul） as a hole conducting material together with an ionic liquid 1-ethyl-3-methylimidazolium bis （trifluoromethylsulfonyl） amide and lithium bis （triflu- oromethanesulfone） imide as additives for charge transport promotion. Dramatic enhancements in the cell performances were observed with the additives in Cul. While the cell sensitized with P3TAA generated a short-circuit photocurrent of -1.45 ***^-2, an open-circuit photovoltage of -345 mV with a total power conversion efficiency of -0.3% under simulated full sunlight of 100 mW-cm^-2 （air mass： 1.5）, the cell sensitized with copolymer P3TAA-PHT delivered -0.25% efficiency under the same conditions with -1.23 mA-cm^-2 as photocurrent and -371 mV as photovoltage.

关键词： Solar cells Polymers Titanium dioxide

Modified strip saturated models for two equal collinear cracks with coalesced zones in piezoelectric media

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Applied Mathematics and Mechanics(English Edition) 2019年第8期40卷 1097-1118页

作者： S.SINGH1 K.SHArMA r.r.BHArGAVA Department of Sciences and Humanities National Institute of Technology Uttarakhand Srinagar 246174India Department of Mathematics Indian Institute of Technology Roorkee Roorkee 247667India

Two equal collinear cracks with coalesced interior electric saturation zones are analytically studied for two-dimensional (2D) arbitrary polarized semipermeable piezo- electric media based on a modified strip saturated model. The strip saturated model is modified here by varying the strip saturated constant electric displacement condition to the polynomially varying electric displacement conditions. Based on the linear, quadratic, and cubic electric displacement conditions on the inner and outer saturated zones, dif- ferent modified strip saturated models are proposed and studied for two equal collinear cracks. With the Stroh formalism and the complex variable technique, these fracture problems are reduced into different types of non-homogeneous riemann Hilbert problems in unknown generalized complex potential functions. These mathematical problems are then solved with the riemann-Hilbert approach to obtain the stress and electric displace- ment components at any point of the domain. The explicit expressions for the outer saturated zone length, the crack opening potential (COP), the crack opening displace- ment (COD), and the local intensity factors (LIFs) are derived. A numerical study is presented for the modified strip saturated model in 2D arbitrary polarized semiperme- able PZT-4 material. The obtained results are compared with those of the strip saturated model, and the effects of the polynomially varying saturation condition on the saturated zones and the applied electrical loadings are presented.

关键词： complex variable coalesced zone piezoelectric riemann-Hilbert problem strip saturated model

Linear and nonlinear torsional free vibration of functionally graded micro/nano-tubes based on modified couple stress theory

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Applied Mathematics and Mechanics(English Edition) 2016年第6期37卷 725-740页

作者： A.r.SETOODEH M.rEZAEI M.r.ZENDEHDEL SHAHrI Faculty of Mechanical and Aerospace Engineering Shiraz University of Technology

The linear and nonlinear torsional free vibration analyses of functionMly graded micro/nuno-tubes （FGMTs） are analytically investigated based on the couple stress theory. The employed non-classical continuum theory contains one material length scale parameter, which can capture the small scale effect. The FGMT model accounts for the through-radius power-law variation of a two-constituent material. Hamilton＇s principle is used to develop the non-classical nonlinear governing equation. To study the effect of the boundary conditions, two types of end conditions, i.e., fixed-fixed and fixed-free, are considered. The derived boundary value governing equation is of the fourthorder, and is solved by the homotopy analysis method （HAM）. This method is based on the Taylor series with an embedded parameter and is capable of providing very good approximations by means of only a few terms, if the initial guess and the auxiliary linear operator are properly selected. The analytical expressions are developed for the linear and nonlinear natural frequencies, which can be conveniently used to investigate the effects of the dimensionless length scale parameter, the material gradient index, and the vibration amplitude on the natural frequencies of FGMTs.

关键词： torsional vibration nonlinear vibration micro/nano-tube functionallygraded material (FGM) couple stress theory size effect

Surface stress effect on the vibration and instability of nanoscale pipes conveying fluid based on a size-dependent Timoshenko beam model

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Acta Mechanica Sinica 2015年第5期31卷 708-719页

作者： r.Ansari r.Gholami A.Norouzzadeh M.A.Darabi Department of Mechanical Engineering University of Guilan Department of Mechanical Engineering Lahijan BranchIslamic Azad University

Presented in this paper is a precise investigation of the effect of surface stress on the vibration characteristics and instability of fluid-conveying nanoscale *** this end,the nanoscale pipe is modeled as a Timoshenko *** equations of motion of the nanoscale pipe are obtained based on Hamilton＇s principle and the Gurtin-Murdoch continuum elasticity incorporating the surface stress ***,the generalized differential quadrature method is employed to discretize the governing equations and associated boundary *** what extent important parameters such as the thickness,material and surface stress modulus,residual surface stress,surface density,and boundary conditions influence the natural frequency of nanoscale pipes and the critical velocity of fluid is discussed.

关键词： Fluid-conveying pipes Vibration and instability Surface stress Gurtin-Murdoch elasticity continuum Generalized differential quadrature method

Heat Transfer Augmentation in Developing Flow Through a ribbed Square Duct

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Journal of Thermal Science 2006年第3期15卷 251-256页

作者： Khan r K Ali M.A.T Akhanda M.A.r Principal Polytechnic InstitutePotuakhaliBangladesh Department of Mechanical Engineering Bangladesh University of Engineering and Technology(BUET)DhakaBangladesh Department of Mechanical and Chemical Engineering Islamic University of Technology(IUT) OIC Gazipur-1704DhakaBangladesh

An experimental study is conducted to investigate the heat transfer augmentation in developing turbulent flow through a ribbed square duct. The duct is made of 16ram thick bakelite sheet. The bottom surface of the ribbed wall having rib pitch to height ratio of 10 is heated by passing a c current to the heater placed under it. The uniform heating is controlled using a digital temperature controller and a variac. The results of ribbed duct are compared with the results of a smooth duct under the same experimental conditions. It is observed that the heat transfer augmentation in ribbed duct is better than that of the smooth duct. At re=5.0× 10^4 , the mean temperature of air flowing through the ribbed duct increases by 2.45 percent over the smooth duct, whereas in the fibbed duct Nusselt number increases by 15.14 percent than that of the smooth duct with a 6 percent increase in pressure drop.

关键词： heat transfer square duct developing flow turbulent promoters

Effect of wall rougheners on cross-sectional flow characteristics for non-spherical particles in a horizontal rotating cylinder

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Particuology 2014年第1期12卷 44-53页

作者： Guang Lu James r.Third Christoph r.Müller ETH Zürich Department of Mechanical and Process Engineering Institute of Energy Technology Laboratory of Energy Science and Engineering8092 Zürich Switzerland

Discrete-element-method （DEM） simulations have been performed to investigate the cross-sectional flow of non-spherical particles in horizontal rotating cylinders with and without wall rougheners. The non-spherical particles were modeled using the three-dimensional super-quadric equation. The influence of wall rougheners on flow behavior of grains was studied for increasing particle blockiness. Moreover, for approximately cubic particles （squareness parameters [555]）, the rotational speed, gravitational acceleration and particle size were altered to investigate the effect of wall rougheners under a range of operating conditions. For spherical and near-spherical particles （approximately up to the squareness parameters [344]）, wall rougheners are necessary to prevent slippage of the bed against the cylinder wall. For highly cubic particle geometries （squareness parameters larger than [3441）, wall rougheners resulted in a counter-intuitive decrease in the angle of repose of the bed. In addition, wall rougheners employed in this study were demonstrated to have a higher impact on bed dynamics at higher rotational speeds and lower gravitational accelerations. Nevertheless, using wall rougheners had a comparatively small influence on particle-flow characteristics for a bed composed of finer grains.

关键词： Granular flowNon-spherical particlesrotating cylinderDiscrete element method (DEM)Kiln