Scientia Iranica
Volume:20 Issue: 6, 2013

This research presents the two-dimensional controlled pushing-based nanomanipulation using an Atomic Force Microscope (AFM). A reliable control of the AFM tip position is crucial to the AFM-based manipulation since the tip can jump over the target nanoparticle causing the process to fail. However, detailed modeling and anunderstanding of the interaction forces on the AFM tip has a central role in this process. In the proposed model, the Lund-Grenoble (LuGre) method is used to model dynamic friction force between the nanoparticle and the substrate. This model leads to stick-slip behavior of the nanoparticle which is in agreement with the experimental behavior at nanoscale. Derjaguin interaction force, which includes both attractive and repulsive interactions, is used to model the contact between the tip and nanoparticle. AFM is modeled by the lumped-parameters model. A controller is designed based on the proposed dynamic model for positioning of the AFM tip during a desired nanomanipulation task. Optimal sliding mode approach is used to design the controller. Performance of the controller is shown by the simulation.

This study has focused on natural convection in an inclined L-shaped cavity filled with copper-water nanofluid. The governing equations including continuity, momentum and energy equations have been discretized with control volume method (FVM) using SIMPLER algorithm. A proper upwinding scheme is employed to obtain stabilized solutions. The effective parameters are solid volume fraction (0≤ φ ≤0.05), inclination angle (0°≤γ≤135°), shape factor (0.6≤2W/L≤1) and Rayleigh number (101≤Ra≤105). Results have been presented as isotherm lines, stream lines, local Nusselt number and average Nusselt number. The effects of Rayleigh number, inclination angle, shape factor as well as solid volume fraction have been investigated on flow field and Nusselt number. Results show that solid volume fraction and shape factor as well as inclination angle have important effect on flow field, especially on average Nusselt number. The results indicate decrease in shape factor and increase in solid volume fraction lead to increase in average Nusselt number.

The development of composite scaffold materials in bone tissue engineering is gaining appeal as beneficial properties of two or more types of materials can be compounded together to achieve better mechanical and physiological demands of the host tissue. In this study, poly (3-hydroxybutyrate) was reinforced with different weight ratio of nanobioglass (0, 2.5, 5, 7.5 and 10 wt %). The nanocomposite scaffolds were successfully prepared by the salt leaching process with various volume fractions of porosities (70, 80 and 90 wt% of NaCl). The results of our studies showed a favorable interaction between polymer and bioglass nanoparticles which improved interfaces and the mechanical property, especially in the samples which were prepared with 70 wt% NaCl. The Young’s modulus of samples ranged from 7.23 MPa to 48.27 MPa, which were in the range of Young’s modulus of cancellous bone. The results analysis of samples which were immersed in SBF, showed that hydroxyapatite formed on the nanocomposite scaffolds’ surfaces, so they exhibit high bioactivity compared to the pure PHB scaffolds. In this study, nanobioglass as a reinforcement phase with low mass fraction can be more effective than micro-materials with high mass fraction in the other studies.

A hybrid continuum-atomistic approach is developed to describe the buckling behavior of axially loaded chiral boron nitride nanotubes (BNNTs) with different boundary conditions. The set of the stability equations is established based on the nonlocal elasticity of Eringen and Donnell shell theory. The molecular mechanics is implemented in conjunction with the density functional theory (DFT) to obtain the effective in-plane and bending stiffnesses and Poisson’s ratio of BNNTs. The problem is analytically solved by the use of a direct variational method. The influences of geometrical parameters, nonlocal parameter and boundary conditions on the critical buckling loads are thoroughly explored.

A cubic to tetragonal structure transition has evolved by substitution of Cu2+ ions in magnesium ferrite, fabricated via the sol-gel method. TEM studies revealed quasi-spherical particles for MgFe2O4 and rod-shaped particles for CuFe2O4, suggesting an enhancement of morphological anisotropy with Cu doping. Thermal analysis shows the formation of MgFe2O4 and CuFe2O4 at ~380 oC and ~340 oC respectively, indicating reduction in temperature for the formation of the samples with copper doping. XRD show the structural transition of cubic to tetragonal structure with increasing copper concentration. The dc electrical resistivity decreases with copper doping in MgFe2O4, attributing to the increase in conductivity due to Cu2+-Cu+ ions hopping. MgFe2O4 has been found to have a saturation magnetization of ~23 emu/g and coercive field of ~54 Oe. The saturation magnetization increases while coercivity initially decreased and then increases with increasing copper concentration.

In this paper, a novel structure for MOSFET like CNTFETs (MOSCNTs) is proposed, combining the advantages of both high and low dielectrics to improve output characteristics. In this structure, the gate dielectric at the drain side is selected from a material with low dielectric constant to form smaller capacitances while a material with high dielectric constant is selected at the source side to improve on current and reduce leakage current. The new structure is simulated based on Schrödinger-Poisson formulation. Obtained results show that the proposed configuration has lower off and higher on current in comparison with low-k MOSCNTs. Also, using a two-dimensional model, a wide range of the new structure performance parameters is studied. It is found that transconductance, intrinsic cut-off frequency and quantum capacitance parameters are improved compared to MOSCNTs with low dielectric constant. It is clear that the proposed structure can provide DIBL and subthreshold swing near its theoretical limit while it also profits from smaller capacitances in gate, drain and source in comparison with high-k MOSCNTs.

This research paper introduces novel structures of mixed CNT bundle (MCB) based non-conventional arrangements of single- and multi-walled carbon nanotubes. Hierarchical equivalent single conductor (ESC) model is used to analyze the propagation delay and power dissipation of CNT bundles. The hierarchical model of MCB considers two types of CNTs, one single-walled CNT (SWCNT) and other multi-walled CNT (MWCNT). ESCmodel of MCB is the combination of ESC models of bundled SWCNT and bundled MWCNT. Initially, simple ESC models of bundled SWCNT and bundled MWCNT are derived considering the parasitic elements like resistance, capacitance and inductance. Later on, these two equivalent models are combined to build up the final ESC model of novel MCBs. It has been observed that the overall delay and power dissipation are reduced by 48.1% and 20.9% respectively for the novel MCB that has horizontal arrangement of SWCNTs and MWCNTs in equal halves.

Synthesis and characterization of ZnO nanorods usinglow power DC thermal plasma was successfully performed. Several tests were conducted using X-ray fluorescence, particle size analyzer, scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The diameter of ZnO nanorods varies from 43nm to 200nm which can be seen from SEM images and its length varies from 160nm to 1000nm. These nanopowders are rod shape as can be seen from TEM images. The XRD data shows a sharp peak at 36.21o which indicates a good crystal growth and agrees well with JCPDS card no. 36-1451. Effects of electrical current variations of 20, 25 and 30 Amperesto the size of ZnO nanorods are also indicated from aspect ratio of about 8.27, 8.44 and 8.81 respectively. The ultraviolet absorption test results show that the ZnO nanorods can absorb UV with the absorbance ranges of300nm and 340nm wave lengths as well as the peak is at the wave length of 311nm. Photoluminescence test confirmsthat the ZnO spectra are in blue emission with the optimum excitation wavelength of 240nm. It can be concluded that this method is well proven in synthesizing high purity compound, UV-block ability and good luminescence ZnO nanorods.

In the present study, dynamic stability of double-walled boron nitride nanotubes (DWBNNTs) including surface stress effects is investigated based on Gurtin-Murdoch continuum theory. Nonlocal piezoelasticity is incorporated into shell theory to develop non-classical model for DWBNNT. The effects of van der Waals (vdW) forces, viscose fluid passes through the inner nanotube and visco-Pasternak medium are evaluated. Fluid-DWBNNT interaction is evaluated considering slip boundary condition and bulk viscosity. Hamilton’s principle is utilized to derive governing equations with regard to von Kármán geometric nonlinearity. Finally incremental harmonic balance method (IHBM) indicates the dynamic instability region (DIR) of DWBNNT.The detailed parametric study is conducted, focusing on the combined effects of the surface parameters, nonlocality, fluid velocity, Knudsen number, thermal changes, vdW forces and surrounding medium on the DIR of DWBNNT. Numerical results indicate that considering surface stress effect shifts the DIR to higher frequency zone.

Sol-gel method is successfully used for synthesis of ZnO nanoparticles doped with different concentrations of Mg. The structure, morphology, chemical composition, optical and antibacterial activity of the nanoparticles were studied as a function of the Mg doping concentration. The synthesized ZnO samples show hexagonal Wurtzite structure, and the phase segregation takes place for 15% amount of doping.TEM images verifies the formation of nanoparticles in the range of 30-55 nm. FTIR and EDS results also confirm the successful incorporation of Mg in ZnO structure. Optical investigation indicates the increase in band gap energy with increase of doping content. The antibacterial activities of the nanosuspensions were tested against Escherichia Coli (Gram negative) and Streptococcus Mutans (Gram Positive) cultures. ZnO:Mg nanosuspension shows high antibacterial activity which slightly decreases with the amount of Mg.

Novel morphologies of carbon nanotubes obtained through solvothermal reaction of various chlorinated solvents in the presence of various catalysts. The reaction mixture including C2Cl4 as solvent and ferrocene as catalyst exhibited the most interesting novel arrangements of carbon nanotubes. Therefore, more characterizations such as Raman spectroscopy and thermogravimetry analysis were performed on the mentioned sample for further investigation on novel pine-tree-like morphology of carbon nanostructures.