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Lipid nanotubes with well-designed cylindrical structures, tunable dimensions and biocompatible membrane surfaces have found potential applications such as templates to create diverse one-dimensional nanostructures and nanocarriers for drug or gene delivery. In this regard, knowing the encapsulation process is of crucial importance for such developments. The aim of this paper is to study the suction and acceptance phenomena of metallic nanoparticles, and in particular silver and gold, inside lipid nanotubes using the continuum approximation and the 6–12 Lennard-Jones potential function. The nanoparticle is modelled as a perfect sphere and the lipid nanotube is assumed to comprise six layers, namely two head groups, two intermediate layers and two tail groups. Analytical expressions are derived through undertaking surface and volume integrals to evaluate van der Waals potential energy and interaction force of a nanoparticle entering a semi-infinite lipid nanotube. These expressions are then employed to determine the suction and acceptance energies of system. To ascertain the accuracy of the proposed analytical expressions, the multiple integrals of van der Waals interactions are evaluated numerically based on the differential quadrature method. A comprehensive study is conducted to get an insight into the effects of different geometrical parameters including radius of nanoparticles, innermost radius of lipid nanotube, head group and tail group thicknesses on the nature of suction and acceptance energies and van der Waals interactions. Numerical results show that maximum suction energy increases by enlarging the nanoparticle size, while it decreases by increasing the head group thickness or the tail group thickness. It is further found that gold nanoparticle experiences higher maximum suction energies inside lipid nanotubes compared to silver nanoparticle. [ABSTRACT FROM AUTHOR]

In this paper, the pre- and post-buckling behavior of beams made of Functionally Graded Materials (FGMs), a mixture of ceramic and metal, under separate mechanical and thermal loading, is studied. To this end, the finite element formulation is established, based on the Euler-Bernoulli beam theory. The effects of geometrical nonlinearity and imperfection are taken into account. The arc-length algorithm is employed to obtain the secondary path beyond the bifurcation point. The influences of material index, imperfection, geometrical parameters and different boundary conditions of simplysupported, clamped-simply and clamped-clamped, on the post-buckling characteristics of FGM beams, are thoroughly investigated. The results generated are compared with the existing data in the literature and good agreements are achieved. The investigation undertaken here proves the necessity of performing post-buckling analysis on FGM beams, especially with simply-supported end conditions. [ABSTRACT FROM AUTHOR]

In this paper, the elasto-plastic pre- and post-buckling behavior of beams made of functionally graded materials subjected to mechanical loading is investigated. A continuum-based finite element formulation is developed to determine the major characteristics of buckling. The arc-length algorithm is employed to analyze the stability problem. A plane stress von Mises model with isotropic hardening is utilized for the elasto-plastic nonlinear analysis of the beam. Basic idea in geometric and material nonlinear analysis of functionally graded material beams is to use the plasticity capacity of metal phase as a ductile material during loading. The influences of number of axial modes, material index, geometrical parameters and boundary conditions on the critical buckling point, pre- and post-buckling paths, plastic bifurcation point and stress distribution are fully studied. A good agreement between generated results and existing data in the literature is observed. [ABSTRACT FROM PUBLISHER]

This article introduces a new semi-analytical nonlinear finite element formulation for thin cylinders according to a continuum-based approach. A comparison between the continuum-based approach and the classical approach for the buckling behavior of isotropic and orthotropic perfect cylinders validates the results. The classical approach is defined according to thin shell theories based on the von Karman approximation. A mathematical modeling for geometry imperfection of cylinders is derived according to a continuum-based approach whose results are compared with the results of the classical approach for imperfect cylinders. The influence of neglecting some nonlinear terms in the classical approach for perfect and imperfect cylinders on the buckling path is investigated. In the buckling analysis, two methods, i.e. the perturbation and load disturbance methods, which undertake to switch to the post-buckling path, are compared to each other. [ABSTRACT FROM PUBLISHER]

In this paper the meshless local Petrov-Galerkin (MLPG) method is implemented to study the buckling of isotropic cylindrical shells under axial load. Displacement field equations, based on Donnell and first order shear deformation theory, are taken into consideration. The set of governing equations of motion are numerically solved by the MLPG method in which according to a semi-inverse method, a new variational trial-functional is constructed to derive the stiffness matrices and critical buckling loads are obtained in various boundary conditions. The moving least squares interpolation is employed to construct both trial and test functions. The present method is a truly meshless method based on a number of randomly located nodes upon which no global background integration mesh is needed and no element matrix assembly is required. In the present MLPG formulation, a local variational form is constructed over a local sub-domain instead of using the conventional weighted-residual procedure. The influences of some commonly used boundary conditions and effects of shell geometrical parameters are studied. The results show the convergence characteristics and accuracy of the mentioned method. [ABSTRACT FROM AUTHOR]