An efficient numerical approach to the micromorphic hyperelasticity

Continuum Mechanics and Thermodynamics - A computationally efficient numerical strategy called as variational differential quadrature-finite element method (VDQFEM) is developed herein for the...     

Studying the buckling and vibration characteristics of single-walled zinc oxide nanotubes using a nanoscale finite element model

The free vibration and axial buckling of achiral zinc oxide nanotubes (ZnONTs) are studied in this paper based on a three-dimensional finite-element model in which bonds are modeled using beam elements and mass elements are placed at the joints of beams instead of atoms. To determine the mechanical properties of the nanotubes, a linkage is established between molecular mechanics and density functional theory. The fundamental frequency and critical buckling load of ZnONTs with different geometries, chiralities and boundary conditions are calculated. It is shown that zigzag nanotubes are more stable than armchair ones. Investigating the effect of aspect ratio on the critical force shows that longer nanotubes are less stable. Also, it is indicated that increasing the length of the nanotubes will result in decreasing the frequency. Moreover, as the aspect ratio increases, the effect of end conditions diminishes.     

Ultrafast electrokinetics

The influence of a high electric field applied on both fluid flow and particle velocities is quantified at large Peclet numbers. The experiments involved simultaneous particle image velocimetry and flow rate measurements. These are conducted in polydimethylsiloxane channels with spherical nonconducting polystyrene particles and DI water as the background flow. The high electric field tests produced up to three orders of magnitude higher electrokinetic velocities than any previous reports. The maximum electroosmotic velocity and electrophoretic velocity measured were 3.55 and 2.3 m/s. Electrophoretic velocities are measured over the range of 100 V/cm < E < 250 000 V/cm. The results are separated according to the different nonlinear theoretical models, including low and high Peclet numbers, and weak and strong concentration polarization. They show good agreement with the models. Such fast velocities could be used for flow separation, mixing, transport, control, and manipulation of suspended particles as well as microthrust generation among other applications.     

Analytical solution approach for nonlinear buckling and postbuckling analysis of cylindrical nanoshells based on surface elasticity theory

The size-dependent nonlinear buckling and postbuckling characteristics of circular cylindrical nanoshells subjected to the axial compressive load are investigated with an analytical approach. The surface energy effects are taken into account according to the surface elasticity theory of Gurtin and Murdoch. The developed geometrically nonlinear shell model is based on the classical Donnell shell theory and the von K′arm′an's hypothesis. With the numerical results, the effect of the surface stress on the nonlinear buckling and postbuckling behaviors of nanoshells made of Si and Al is studied. Moreover, the influence of the surface residual tension and the radius-to-thickness ratio is illustrated.The results indicate that the surface stress has an important effect on prebuckling and postbuckling characteristics of nanoshells with small sizes.     

Studying linear and nonlinear vibrations of fractional viscoelastic Timoshenko micro-/nano-beams using the strain gradient theory

Nonlinear Dynamics - In this paper, the vibrational behavior of micro- and nano-scale viscoelastic beams under different types of end conditions in the linear and nonlinear regimes is investigated...     

Highly Efficient Synthesis and Assay of Protein‐Imprinted Nanogels by Using Magnetic Templates

We report an approach integrating the synthesis of protein‐imprinted nanogels (“plastic antibodies”) with a highly sensitive assay employing templates attached to magnetic carriers. The enzymes trypsin and pepsin were immobilized on amino‐functionalized solgel‐coated magnetic nanoparticles (magNPs). Lightly crosslinked fluorescently doped polyacrylamide nanogels were subsequently produced by high‐dilution polymerization of monomers in the presence of the magNPs. The nanogels were characterised by a novel competitive fluorescence assay employing identical protein‐conjugated nanoparticles as ligands to reversibly immobilize the corresponding nanogels. Both nanogels exhibited K_d<10 pM for their respective target protein and low cross‐reactivity with five reference proteins. This agrees with affinities reported for solid‐phase‐synthesized nanogels prepared using low‐surface‐area glass‐bead supports. This approach simplifies the development and production of plastic antibodies and offers direct access to a practical bioassay.     

Quantum chemical study of the interaction between selenium analog of methimazole as an anti-thyroid drug and metal cations

Energetic and structural properties of complexes formed from interaction between selenium analog of methimazole (MSeI) as an anti-thyroid drug and M^z+ (Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺ and Ca²⁺) cations have been investigated using B3LYP, M062X, PBE1PBE, and MP2 methods with 6-311++G(d,p) and 6-311++G(2d,2p) basis sets. Two planar and perpendicular complexes were predicted from interaction of MSeI and M^z+ cations. From the Gibbs free energy difference between the planar and perpendicular forms of MSeI–M^z+ complexes, it is found that the perpendicular forms are the predominant ones. In addition, the comparison of interaction energies shows that the order of energies increases in the following order: K⁺ < Na⁺ < Li⁺ < Ca²⁺ < Mg²⁺ < Be²⁺. The results of natural bond orbital analysis showed that the charge transfer occurs from MSeI to metal cations. The atom in molecule analysis shows that the charge density and its Laplacian at the Se–M^z+ bond critical point of the MSeI–M²⁺ complexes are greater than the MSeI–M¹⁺ ones. Also, it was revealed that the Se–M^z+ interactions in perpendicular complexes of alkali and alkaline metal cations are electrostatic and partially covalent in nature, respectively.     

Explicit analytical expressions for the critical buckling stresses in a monolayer graphene sheet based on nonlocal elasticity

Explicit expressions are given to study the biaxial buckling of monolayer graphene sheets. Based upon the continuum mechanics, a plate model is adopted in which the small length scale effect is incorporated into the governing equation through the nonlocal elasticity theory of Eringen. By employing the Galerkin method, analytical expressions are derived which allow quick and accurate calculation of the critical buckling loads of monolayer graphene sheets with various boundary conditions from the static deflection under a uniformly distributed load. The effectiveness of the present study is assessed by molecular dynamics simulations as a benchmark of good accuracy.