Search for: inhomogeneities
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    An inhomogeneous model universe behaving homogeneously

    , Article General Relativity and Gravitation ; Volume 40, Issue 5 , 2008 , Pages 1047-1069 ; 00017701 (ISSN) Khosravi, Sh ; Kourkchi, E ; Mansouri, R ; Akrami, Y ; Sharif University of Technology
    We present a new model universe based on the junction of FRW to flat Lemaitre-Tolman-Bondi (LTB) solutions of Einstein equations along our past light cone, bringing structures within the FRW models. The model is assumed globally to be homogeneous, i.e. the cosmological principle is valid. Local inhomogeneities within the past light cone are modeled as a flat LTB, whereas those outside the light cone are assumed to be smoothed out and represented by a FRW model. The model is singularity free, always FRW far from the observer along the past light cone, gives way to a different luminosity distance relation as for the CDM/FRW models, a negative deceleration parameter near the observer, and... 

    Calibration of forming limit diagrams using a modified Marciniak-Kuczynski model and an empirical law

    , Article Materials and Design ; Volume 34 , Feb , 2012 , Pages 185-191 ; 02641275 (ISSN) Ghazanfari, A ; Assempour, A ; Sharif University of Technology
    The major problem in determining the forming limit diagram (FLD) with the Marciniak-Kuczynski (M-K) model is the necessity of an experimental point in order to find the initial inhomogeneity coefficient and calibrate the diagram. The purpose of the present work is to eliminate this requirement. To do this, the usual assumption of geometrical inhomogeneity has been replaced with material inhomogeneity and it has been shown that the sensitivity of the diagram to variations of the inhomogeneity factor is reduced greatly with the new assumption. Using this advantage and collecting enough experimental data for different materials, an empirical law in terms of sheet thickness has been proposed... 

    Polyelectrolytes polarization in nonuniform electric fields

    , Article International Journal of Modern Physics C ; Volume 25, Issue 12 , 2014 ; ISSN: 17936586 Farahpour, F ; Ejtehadi, M. R ; Varnik, F ; Sharif University of Technology
    Stretching dynamics of polymers in microfluidics is of particular interest for polymer scientists. As a charged polymer, a polyelectrolyte (PE) can be deformed from its coiled equilibrium configuration to an extended chain by applying uniform or nonuniform electric fields. By means of hybrid lattice Boltzmann (LB)-molecular dynamics (MD) simulations, we investigate how the condensed counterions (CIs) around the PE contribute to the polymer stretching in inhomogeneous fields. As an application, we discuss the translocation phenomena and entropic traps, when the driving force is an applied external electric field  

    Modified averaging processes in cosmology and the structured frw model

    , Article International Journal of Modern Physics D ; Volume 18, Issue 7 , 2009 , Pages 1177-1192 ; 02182718 (ISSN) Khosravi, S ; Mansouri, R ; Kourkchi, E ; Sharif University of Technology
    We study the volume averaging of inhomogeneous metrics within GR and discuss its shortcomings, such as gauge dependence, singular behavior as a result of caustics, and causality violations. To remedy these shortcomings, we suggest some modifications to this method. As a case study we focus on the inhomogeneous structured FRW model based on a flat LTB metric. The effect of averaging is then studied in terms of an effective backreaction fluid. It is shown that, contrary to the claims in the literature, the backreaction fluid behaves like a dark matter component, instead of dark energy, having a density of the order of 10-5 times the matter density, and, most importantly, it is gauge-dependent.... 

    Analytical solution of wave equation for arbitrary non-homogeneous media

    , Article Electro-Optical System Design, Simulation, Testing and Training, Seattle, WA, 9 July 2002 through 10 July 2002 ; Volume 4772 , 2002 , Pages 25-36 ; 0277786X (ISSN) Khorasani, S ; Mehrany, K ; SPIE ; Sharif University of Technology
    We present a new analytical method for solution of 1?D quantum and optical systems, based on the differential transfer matrices. This approach can be used for exact calculation of various functions including reflection and transmission coefficients, band structures as well as bound states. We show the consistency of WKB method with out approach and discuss improvements for even symmetry and infinite periodic structures. Moreover a general variational representation of bound states is introduced. As application examples, we consider several test cases including the reflection and band structure of gratings as well as bounded states of inhomogeneous waveguides. An excellent agreement between... 

    Composites with superspherical inhomogeneities

    , Article Philosophical Magazine Letters ; Volume 89, Issue 7 , 2009 , Pages 439-451 ; 09500839 (ISSN) Hashemi, R ; Avazmohammadi, R ; Shodja, H. M ; Weng, G. J ; Sharif University of Technology
    In contrast to the traditional study of composites containing ellipsoidal inclusions, we highlight some calculated results for the effective moduli when the inclusion shape can be described by the superspherical equation, [image omitted], such that when p = 2 it reduces to a sphere and when p it becomes a perfect cube. We consider the cases of both aligned and randomly oriented superspherical inclusions with isotropic, cubic, and transversely isotropic properties, and show how the shape parameter, p, affects the overall moduli of the composites during the spherical to cuboidal transition  

    Inhomogeneity through warm equal channel angular pressing

    , Article Journal of Materials Engineering and Performance ; Volume 22, Issue 6 , 2013 , Pages 1666-1671 ; 10599495 (ISSN) Vaseghi, M ; Kim, H. S ; Karimi Taheri, A ; Momeni, A ; Sharif University of Technology
    In this study, the hardness inhomogeneity of billets during multi-passes of equal channel angular pressing (ECAP) at elevated temperatures is investigated and the effect of large strain deformation during ECAP on the hardness inhomogeneity characteristics due to dynamic aging of aluminum 6061 under a variety of temperatures and ram speed was studied by TEM and hardness measurements. The hardness results showed that the hardness distribution is more homogenous after four passes using the pressing route Bc. However, when the deformation temperature was considered, performing ECAP at 100 C may provide the most homogeneous microstructure after multi-pressing as long as the total number of... 

    3D elastodynamic fields of non-uniformly coated obstacles: Notion of eigenstress and eigenbody-force fields

    , Article Mechanics of Materials ; Volume 41, Issue 9 , 2009 , Pages 989-999 ; 01676636 (ISSN) Shodja, H. M ; Delfani, M. R ; Sharif University of Technology
    Based on wave-function expansion, the time harmonic wave scattered by a circular and spherical inhomogeneity has been studied by numerous investigators. This method has also been employed to axisymmetrically coated circular and spherical inhomogeneities by some authors. When the geometry of the obstacle is not axisymmetric, the wave-function expansion is no longer applicable. In this paper, it is proposed to employ the dynamic equivalent inclusion method (DEIM) which is more general than the methods presented in the literature. It will be seen that DEIM may be used to treat a wide range of situations in a unified manner and is not bound to certain symmetries. The DEIM was first proposed by... 

    The noise equivalent circuit model of quantum-dot lasers

    , Article Journal of Russian Laser Research ; Volume 33, Issue 3 , May , 2012 , Pages 217-226 ; 10712836 (ISSN) Horri, A ; Mirmoeini, S. Z ; Faez, R ; Sharif University of Technology
    We derive the noise equivalent circuit model of semiconductor self-assembled quantum-dot (QD) lasers (SAQDL) from the rate equations including Langevin noise sources. This equivalent circuit allows a straightforward calculation of the noise of an SAQDL combined with electronic components. Using the presented model, we study how the carrier dynamics influences relative intensity noise (RIN) of QD lasers. We demonstrate that RIN is degraded with larger inhomogeneous broadening. Furthermore, we show that RIN is enhanced for lower quantum-dot coverage level  

    Deformation inhomogeneity in flattened copper wire

    , Article Materials and Design ; Volume 28, Issue 7 , 2007 , Pages 2047-2053 ; 02613069 (ISSN) Kazeminezhad, M ; Karimi Taheri, A ; Sharif University of Technology
    Elsevier Ltd  2007
    The deformation inhomogeneity in flattened wire produced by the wire flat rolling process is studied. Utilizing the combined Finite and Slab Element Method (FSEM), the effective strain fields in the flattened wire are calculated at different reductions in height and frictional conditions and compared with experiment. The calculated and experimental results exhibit that the deformation is inhomogeneous and macroscopic shear bands are appeared in the cross section of flattened wire. Using the results of the analysis, it is shown that the deformation inhomogeneity, introduced by an Inhomogeneity Factor (IF), is different on the x-axis and y-axis in the cross section of the flattened wire. By... 

    Determination of strain field and heterogeneity in radial forging of tube using finite element method and microhardness test

    , Article Materials and Design ; Volume 38 , June , 2012 , Pages 147-153 ; 02641275 (ISSN) Sanjari, M ; Saidi, P ; Karimi Taheri, A ; Hossein Zadeh, M ; Sharif University of Technology
    Utilizing the Finite Element Method (FEM), the strain field in the radial forging process of tube is calculated at different process conditions and compared with the experimental results achieved using the microhardness test. The effect of various process parameters such as friction, axial feed, back push and front pull forces and die angles on the strain field are investigated. Using the results of the analysis, it is shown that the deformation inhomogeneity, introduced by an Inhomogeneity Factor (IF), is maximum in the inner zone of tube, while the minimum and the maximum effective strains are appeared at the inner zone of tube and about the core of the tube thickness, respectively. Also,... 

    The scattering of P-waves by a piezoelectric particle with FGPM interfacial layers in a polymer matrix

    , Article International Journal of Solids and Structures ; Volume 47, Issue 18-19 , 2010 , Pages 2390-2397 ; 00207683 (ISSN) Kamali, M. T ; Shodja, H. M ; Sharif University of Technology
    Propagation of P-wave in an unbounded elastic polymer medium which contains a set of nested concentric spherical piezoelectric inhomogeneities is formulated. The polymer matrix is made of Epoxy and is isotropic; each phase of the inhomogeneity is made of a different piezoelectric material and is radially polarized and has spherical isotropy. Note that the individual phases are homogeneous, and all interfaces are perfectly bonded. The scattered displacement and electric potentials in the matrix are expressed in terms of spherical wave vector functions and Legendre functions, respectively. The transmitted displacement and electric potentials within each phase of the piezoelectric particle are... 

    A screw dislocation near a damaged arbitrary inhomogeneity–matrix interface

    , Article International Journal of Damage Mechanics ; Volume 29, Issue 2 , 2020 , Pages 272-296 Kamali, M. T ; Shodja, H. M ; Masoudvaziri, N ; Sharif University of Technology
    SAGE Publications Ltd  2020
    In the literature, the analytical solutions concerned with the interaction between screw dislocation and surfaces/interfaces have been mainly limited to simple geometries and perfect interfaces. The focus of the current work is to provide an approach based on a rigorous semi-analytical theory suitable for treatment of such surfaces/interfaces that concurrently have complex geometry and imperfect bonding. The proposed approach captures the singularity of the elastic fields exactly. A vast variety of the pertinent interaction problems such as dislocation near a multi-inhomogeneity with arbitrary geometry bonded imperfectly to a matrix, dislocation near the free boundaries of a finite elastic... 

    Interaction of a screw dislocation and an embedded nonuniformly coated circular fiber with imperfect interfaces

    , Article International Journal of Solids and Structures ; Volume 182-183 , 2020 , Pages 295-306 Kamali, M. T ; Shodja, H. M ; Sharif University of Technology
    Elsevier Ltd  2020
    The eccentricity between the circular fiber and its coating as well as the imperfection at the fiber-coating-matrix interfaces associated with certain composites can have a remarkable effect on the movement of a dislocation. For an in-depth understanding of such phenomena, the present work provides an exact analytical solution for the interaction between an eccentrically coated circular inhomogeneity embedded in an infinite elastic medium with imperfect interfaces and a screw dislocation. The dislocation may be located inside one of the regions: the core inhomogeneity, coating, or the matrix. The corresponding boundary value problem is solved by using conformal mapping and complex potential... 

    Novel theories on magneto-electro-elastic ellipsoidal multi-inclusions and inhomogeneities and associated impotent fields

    , Article Mechanics of Materials ; Volume 143 , 2020 Rashidinejad, E ; Shodja, H. M ; Sharif University of Technology
    Elsevier B.V  2020
    The exact nature of the induced coupled-fields of anisotropic magneto-electro-elastic ellipsoidal inclusions, multi-inclusions, and inhomogeneities with non-uniform eigenfields under polynomial magneto-electro-elastic far-field loadings is of particular interest. For the sake of prediction of the induced coupled-fields of magneto-electro-elastic multi-inclusions due to piecewise polynomial generalized eigenfields several theorems and corollaries are stated and proved. Some classes of impotent generalized eigenfields associated with encapsulated ellipsoidal multi-inclusion result in vanishing generalized disturbance strains within the innermost ellipsoidal domain. On the other hand, it is... 

    Surface electromagnetic waves supported by nano conducting layers with inhomogeneities in the conductivity profile

    , Article Optical and Quantum Electronics ; Volume 40, Issue 1 , 2008 , Pages 23-40 ; 03068919 (ISSN) Sarrafi, P ; Mehrany, K ; Sharif University of Technology
    Conducting interfaces and nano conducting layers can support surface electromagnetic waves. Uniform charge layers of non-zero thickness and their asymptotic behavior toward conducting interfaces of infinitely small thicknesses, where the thin charge layer is modeled via a surface conductivity σ s , are already studied. Here, the possible effects of inhomogeneity in the conductivity profile of the thin conducting layers are investigated for the first time and a new approximate yet accurate enough analytical formulation for mode extraction in such structures is given. In order to rigorously analyze the structure and justify the proposed approximate formulation, the Galerkin's method with... 

    Studying the Interaction Between Dislocation Sandin Homogeneities in Nano-Scale, by Incorporating Surface Effect

    , M.Sc. Thesis Sharif University of Technology Ahmadzadeh Bakhshayesh, Hossein (Author) ; Mohammadi Shodja, Hossein (Supervisor)
    By considering the effect of surface/interface stress, classical problems of the interaction between dislocations and inhomogeneities are addressed. Especifically two distinct problems are solved, the first one is consisted of an edge dislocation located near an elliptical nano-inhomogeneity and the second one hasa screw dislocation laid in the core-shell nanowire. The stress field as well as the image force on the dislocation are calculated and discussed in detail. Results show that by decreasing the dimension of the problem to nano-scale, the differences between classical elasticity and surface approachincrease rapidly. By considering the effect of the surface/interface stress, new... 

    Multi-resolution Multiscale Finite Volume Method for Reservoir Simulation

    , Ph.D. Dissertation Sharif University of Technology Mosharaf Dehkordi, Mehdi (Author) ; Taghizadeh Manzari, Mehrdad (Supervisor)
    Many of natural porous media, especially oil reservoirs, have strong heterogeneities that span a wide range of scales. These heterogeneities are manifested in the form of strong variations in the permeability field. These variations can be of several orders of magnitude within a small distance. Therefore, the flow in porous media is a multiscale Phenomenon. Due to prohibitive size of input data, numerical simulation of such problems needs extremely large computer memory and computational time, which can be impractical in some cases. In recent years, multiscale methods as a powerful tool have been employed to tackle this problem. In present study, a family of non-iterative Multiscale Finite... 

    A general unified treatment of lamellar inhomogeneities

    , Article Engineering Fracture Mechanics ; Volume 74, Issue 9 , 2007 , Pages 1499-1510 ; 00137944 (ISSN) Shodja, H. M ; Ojaghnezhad, F ; Sharif University of Technology
    Consider a lamellar inhomogeneity embedded in an unbounded isotropic elastic medium. When the elastic moduli of the lamellar inhomogeneity are zero it is a crack, if its elastic moduli are infinite it is an anticrack, and when its elastic moduli are finite it is called a quasicrack. Based on the Eshelby's equivalent inclusion method (EIM), the present paper develops a unified approach for determination of the exact closed-form expressions for modes I, II, and III stress intensity factors (SIFs) at the tips of lamellar inhomogeneities under a remote applied polynomial loading. © 2006 Elsevier Ltd. All rights reserved  

    Itinerant electron transport in microscopically inhomogeneous magnetic fields

    , Article Journal of Magnetism and Magnetic Materials ; Volume 299, Issue 2 , 2006 , Pages 356-361 ; 03048853 (ISSN) Nasirpouri, F ; Nogaret, A ; Atkinson, D ; Ghorbani, M ; Iraji Zad, A ; Sharif University of Technology
    We report on magnetoresistance measurements in thin nickel films modulated by a periodic magnetic field emanating from micromagnetic arrays fabricated at the film surface. By increasing the strength of the magnetic potential using nickel and dysprosium micromagnets, we are able to quench the anisotropic magnetoresistance (AMR) in the film. © 2005 Elsevier B.V. All rights reserved