Showing papers by "Amin Hadi published in 2019"

Thermoelastic analysis of rotating functionally graded micro/nanodisks of variable thickness

Abstract: In this study, stress distribution in a functionally graded nanodisk of variable thickness is investigated based on the strain gradient theory. It is assumed that nanodisk is subjected to thermal and mechanical loads while it is rotating with a constant angular velocity. The equilibrium equation and the corresponding boundary conditions are deduced using Hamilton's principle. A numerical scheme is used to solve the problem. The effects of angular velocity, thickness profile, material inhomogeneity parameter, external loads and temperature are investigated on the total stresses as well as radial displacements. A close examination of the results based on strain gradient and classical theories predict the same trend for variation in radial displacements along the nanodisk radius. Additionally, results show that selection of a variable thickness reduces the radial stresses. Due to coupling effect between radial stress, σ r , and high-order stresses which appear in strain gradient theory, total radial stresses at the inner and outer radii are nonzero despite the zero external loads applied at the two corresponding surfaces. Moreover, Due to very small radius of the nanodisk, the centrifugal forces due to angular velocity ω are negligible and hence, the total radial stresses are barely affected by their magnitudes.

Influence of initial edge displacement on the nonlinear vibration, electrical and magnetic instabilities of magneto-electro-elastic nanofilms

Abstract: A scale-dependent continuum model is presented to investigate the effect of initial in-plane edge displacement on the nonlinear vibration and electromagnetic buckling of magneto-electro-elastic (ME...

Primary and secondary resonance analysis of porous functionally graded nanobeam resting on a nonlinear foundation subjected to mechanical and electrical loads

Abstract: Nonlinear free and forced vibration behavior of a porous functionally graded Euler-Bernoulli nanobeam subjected to mechanical and electrical loads is studied based on the nonlocal strain gradient elasticity theory. It is assumed that the porous functionally graded (FG) nanobeam is resting on a nonlinear foundation. Also, material properties of the nanobeam are assumed to vary in the thickness direction. Equations of motion are derived using Hamilton's principle. Galerkin method along with variation iteration method (VIM), Homotopy perturbation method (HPM), Hamiltonian approach method (HAM) and multiple scale method are employed to solve the governing equations based on clamped-clamped, simply-simply and clamped-simply boundary conditions. For verification purposes, the results of this study are compared with those of other studies. The effects of different parameters such as type of porosity distribution, nonlinear foundation, boundary conditions, electrical voltage and size effect parameters on the primary and secondary resonances were investigated. It was found that length-scale parameters have a crucial role on the nonlinear vibration behavior of such structures.

Effects of stretching on molecular transfer from cell membrane by forming pores

Abstract: Cell function was incessantly regulated by several microenvironments that were dependent on chemical and physical interactions. Physical forces, such as compressive stress, shear stress, an...

Combination of Mechanical and Chemical Methods Improves Gene Delivery in Cell-based HIV Vaccines.

Abstract: Objective Novel vaccination approaches are required to control human immunodeficiency virus (HIV) infections. The membrane proximal external region (MPER) of Env gp41 subunit and the V3/glycans of Env gp120 subunit were known as potential antigenic targets for anti-HIV-1 vaccines. In this study, we prepared the modified dendritic cells (DCs) and mesenchymal stem cells (MSCs) with HIV-1 MPER-V3 gene using mechanical and chemical approaches. Methods At first, MPER-V3 fusion DNA delivery was optimized in dendritic cells (DCs) and mesenchymal stem cells (MSCs) using three mechanical (i.e., uniaxial cyclic stretch, equiaxial cyclic stretch and shear stress bioreactors), and two chemical (i.e., TurboFect or Lipofectamine) methods. Next, the modified DCs and MSCs with MPER-V3 antigen were compared to induce immune responses in vivo. Results Our data showed that the combination of equiaxial cyclic stretch loading and lipofectamine twice with 48 h intervals increased the efficiency of transfection about 60.21 ± 1.05 % and 65.06 ± 0.09 % for MSCs and DCs, respectively. Moreover, DCs and MSCs transfected with MPER-V3 DNA in heterologous DC or MSC prime/ peptide boost immunizations induced high levels of IgG2a, IgG2b, IFN-γ and IL-10 directed toward Th1 responses as well as an increased level of Granzyme B. Indeed, the modified MSCs and DCs with MPER-V3 DNA could significantly enhance the MPER/V3-specific T-cell responses compared to MPER/V3 peptide immunization. Conclusions These findings showed that the modified MSC-based immunization could elicit effective immune responses against HIV antigen similar to the modified DC-based immunization.

Revealing electrical stresses acting on the surface of protoplast cells under electric field

Abstract: When cells exposed to an electric field, localized changes in the distribution of the electric field will be induced and these changes in turn lead to electrical stresses on cell surface. The electrical stresses play a key role in the cell membrane structural changes which leads to important phenomena like hydrophilic pores formation on the cell membrane resulting in the cell permeability. In this work, protoplast cell interaction with direct current (DC) electric field is investigated. The electrical stresses acted on the cell membrane in the presence of electric field are investigated numerically by a modified finite difference method, fast Immersed Interface Method (IIM). Exact solution of dielectrophoresis (DEP) force applied on a cell under a non-uniform electric field is obtained to verify numerical solution obtained by the fast IIM. The numerical results reveal that both mismatched permittivity between cell and insulating suspension fluid and the applied voltage are essential for generating and tuning the total stresses exerted on cell surface. This paper can help to analytically study the electroporation phenomenon which its exact mechanism is still unclear.