alireza aghaei - Academia.edu (original) (raw)

Papers by alireza aghaei

Research paper thumbnail of Sorting ZnO particles of different shapes with low frequency AC electric fields

Materials Letters, 2011

... MANUSCRIPT Sorting ZnO particles of different shapes with low frequency AC electric fields Re... more ... MANUSCRIPT Sorting ZnO particles of different shapes with low frequency AC electric fields Reza Riahifar1, Ehsan Marzbanrad1, , Babak Raissi1, Cyrus Zamani2, Mahmood Kazemzad1Alireza Aghaie1, 1 ... 9] Gardeshzadeh AR, Raissi B, Marzbanrad E, Mohebbi H. Fabrication ...

Research paper thumbnail of Thermodynamics and molecular dynamics investigation of a possible new critical size for surface and inner cohesive energy of Al nanoparticles

Journal of Nanoparticle Research

In this study, the authors first review the previously developed, thermodynamics-based theory for... more In this study, the authors first review the previously developed, thermodynamics-based theory for size dependency of the cohesion energy of free-standing spherically shaped Al nanoparticles. Then, this model is extrapolated to the cubic and truncated octahedron Al nanoparticle shapes. A series of computations for Al nanoparticles with these two new shapes are presented for particles in the range of 1–100 nm. The thermodynamics computational results reveal that there is a second critical size around 1.62 and 1 nm for cubes and truncated octahedrons, respectively. Below this critical size, particles behave as if they consisted only of surface-energy-state atoms. A molecular dynamics simulation is used to verify this second critical size for Al nanoparticles in the range of 1–5 nm. MD simulation for cube and truncated octahedron shapes shows the second critical point to be around 1.63 and 1.14 nm, respectively. According to the modeling and simulation results, this second critical size seems to be a material property characteristic rather than a shape-dependent feature.

Research paper thumbnail of Stability and size-dependency of Cauchy–Born hypothesis in three-dimensional applications

International Journal of Solids and Structures, 2009

The Cauchy-Born hypothesis (CB) provides a hierarchical approach in the molecular theory of cryst... more The Cauchy-Born hypothesis (CB) provides a hierarchical approach in the molecular theory of crystal elasticity to relate the continuum and atomic deformations. This kinematic theory has been extensively used as the constitutive law of continuum regions in multi-scale models. In these models, the fine scale is proposed to describe the real behavior of crystalline structure wherever the continuum description fails. The main objective of this article is to investigate the stability and size-dependency of CB hypothesis in three-dimensional applications by direct comparison of information between atomistic and continuous description of a medium. The Sutton-Chen many-body potential is used for the gold metal to consider the real metallic behavior in numerical simulations. Two failure criteria are introduced in the strain and stress domains; the validity surfaces are derived for the Cauchy-Born hypothesis; and the size effect of specimens is investigated on the convergency of results. It is shown that the gold crystal deforms homogeneously inside the validity surface, in which the material is elastic and the CB has remained valid. It is observed that although the deformation is inhomogeneous and the CB is invalid outside the validity surface, the crystalline structure may exhibit elastic or plastic behavior in this region. Moreover, it is numerically shown that the size-dependency of validity surface decreases with the increase of the size of specimens. These observations are meticulously investigated by loading and unloading several cubic specimens using molecular dynamics simulation.

Research paper thumbnail of Multi-scale modeling of surface effect via the boundary Cauchy-Born method

International Journal for Numerical Methods in Engineering, 2010

In this paper, a novel multi-scale approach is developed for modeling of the surface effect in cr... more In this paper, a novel multi-scale approach is developed for modeling of the surface effect in crystalline nano-structures. The technique is based on the Cauchy–Born hypothesis in which the strain energy density of the equivalent continua is calculated by means of inter-atomic potentials. The notion of introducing the surface effect in the finite element method is based on the intrinsic function of quadratures, called as an indicator of material behavior. The information of quadratures is derived by interpolating the data from probable representative atoms in their proximity. The technique is implemented by the definition of reference boundary CB elements, which enable to capture not only the surface but also the edge and corner effects. As the surface effect is important in small-scale simulation, the relative number of boundary CB elements increases which leads to predomination of boundary effects in the model. In order to implement the equivalent continua in boundary value problems, the updated-Lagrangian formulation of nonlinear finite element is derived. The numerical simulation of the proposed model together with the direct comparison with fully atomistic model indicates that the technique provides promising results for facile modeling of boundary effects and investigating its effect on the mechanical response of metallic nano-scale devices. Copyright © 2010 John Wiley & Sons, Ltd.

Research paper thumbnail of Silica aerogel–iron oxide nanocomposites: recoverable catalysts for the oxidation of alcohols with hydrogen peroxide

Transition Metal Chemistry, 2011

Various aerogels of silica gel doped with Fe2O3 were prepared by sol–gel method. They were calcin... more Various aerogels of silica gel doped with Fe2O3 were prepared by sol–gel method. They were calcined to produce nanoparticle solids. The nanosized mixed oxides were active in the oxidation of alcohols and produced carbonyl compounds in very good to excellent yields using hydrogen peroxide.

Research paper thumbnail of Sorting ZnO particles of different shapes with low frequency AC electric fields

Materials Letters, 2011

... MANUSCRIPT Sorting ZnO particles of different shapes with low frequency AC electric fields Re... more ... MANUSCRIPT Sorting ZnO particles of different shapes with low frequency AC electric fields Reza Riahifar1, Ehsan Marzbanrad1, , Babak Raissi1, Cyrus Zamani2, Mahmood Kazemzad1Alireza Aghaie1, 1 ... 9] Gardeshzadeh AR, Raissi B, Marzbanrad E, Mohebbi H. Fabrication ...

Research paper thumbnail of Thermodynamics and molecular dynamics investigation of a possible new critical size for surface and inner cohesive energy of Al nanoparticles

Journal of Nanoparticle Research

In this study, the authors first review the previously developed, thermodynamics-based theory for... more In this study, the authors first review the previously developed, thermodynamics-based theory for size dependency of the cohesion energy of free-standing spherically shaped Al nanoparticles. Then, this model is extrapolated to the cubic and truncated octahedron Al nanoparticle shapes. A series of computations for Al nanoparticles with these two new shapes are presented for particles in the range of 1–100 nm. The thermodynamics computational results reveal that there is a second critical size around 1.62 and 1 nm for cubes and truncated octahedrons, respectively. Below this critical size, particles behave as if they consisted only of surface-energy-state atoms. A molecular dynamics simulation is used to verify this second critical size for Al nanoparticles in the range of 1–5 nm. MD simulation for cube and truncated octahedron shapes shows the second critical point to be around 1.63 and 1.14 nm, respectively. According to the modeling and simulation results, this second critical size seems to be a material property characteristic rather than a shape-dependent feature.

Research paper thumbnail of Stability and size-dependency of Cauchy–Born hypothesis in three-dimensional applications

International Journal of Solids and Structures, 2009

The Cauchy-Born hypothesis (CB) provides a hierarchical approach in the molecular theory of cryst... more The Cauchy-Born hypothesis (CB) provides a hierarchical approach in the molecular theory of crystal elasticity to relate the continuum and atomic deformations. This kinematic theory has been extensively used as the constitutive law of continuum regions in multi-scale models. In these models, the fine scale is proposed to describe the real behavior of crystalline structure wherever the continuum description fails. The main objective of this article is to investigate the stability and size-dependency of CB hypothesis in three-dimensional applications by direct comparison of information between atomistic and continuous description of a medium. The Sutton-Chen many-body potential is used for the gold metal to consider the real metallic behavior in numerical simulations. Two failure criteria are introduced in the strain and stress domains; the validity surfaces are derived for the Cauchy-Born hypothesis; and the size effect of specimens is investigated on the convergency of results. It is shown that the gold crystal deforms homogeneously inside the validity surface, in which the material is elastic and the CB has remained valid. It is observed that although the deformation is inhomogeneous and the CB is invalid outside the validity surface, the crystalline structure may exhibit elastic or plastic behavior in this region. Moreover, it is numerically shown that the size-dependency of validity surface decreases with the increase of the size of specimens. These observations are meticulously investigated by loading and unloading several cubic specimens using molecular dynamics simulation.

Research paper thumbnail of Multi-scale modeling of surface effect via the boundary Cauchy-Born method

International Journal for Numerical Methods in Engineering, 2010

In this paper, a novel multi-scale approach is developed for modeling of the surface effect in cr... more In this paper, a novel multi-scale approach is developed for modeling of the surface effect in crystalline nano-structures. The technique is based on the Cauchy–Born hypothesis in which the strain energy density of the equivalent continua is calculated by means of inter-atomic potentials. The notion of introducing the surface effect in the finite element method is based on the intrinsic function of quadratures, called as an indicator of material behavior. The information of quadratures is derived by interpolating the data from probable representative atoms in their proximity. The technique is implemented by the definition of reference boundary CB elements, which enable to capture not only the surface but also the edge and corner effects. As the surface effect is important in small-scale simulation, the relative number of boundary CB elements increases which leads to predomination of boundary effects in the model. In order to implement the equivalent continua in boundary value problems, the updated-Lagrangian formulation of nonlinear finite element is derived. The numerical simulation of the proposed model together with the direct comparison with fully atomistic model indicates that the technique provides promising results for facile modeling of boundary effects and investigating its effect on the mechanical response of metallic nano-scale devices. Copyright © 2010 John Wiley & Sons, Ltd.

Research paper thumbnail of Silica aerogel–iron oxide nanocomposites: recoverable catalysts for the oxidation of alcohols with hydrogen peroxide

Transition Metal Chemistry, 2011

Various aerogels of silica gel doped with Fe2O3 were prepared by sol–gel method. They were calcin... more Various aerogels of silica gel doped with Fe2O3 were prepared by sol–gel method. They were calcined to produce nanoparticle solids. The nanosized mixed oxides were active in the oxidation of alcohols and produced carbonyl compounds in very good to excellent yields using hydrogen peroxide.