Scientia Iranica
Volume:21 Issue: 3, 2014

Buoyancy-driven heat transfer due to a square-shaped heater placed inside a square cavity filled with the TiO2-water nanofluid is investigated numerically. The heater is maintained at a constant temperature Th while the cavity walls are kept at a lower constant temperature Tc. The governing equations are solved using the finite volume method and the SIMPLER algorithm. The simulations are performed for six different positions of the heat source inside the cavity, a range of Rayleigh numbers from 103 to 106, and different volume fractions of the nanoparticles. The ratio of the height (width) of the heat source to that of the cavity is taken as 0.2. The results shows that the fluid flow and heat transfer characteristics inside the cavity strongly depend on the location of the heat source. For Ra = 103, i.e., conduction-dominated heat transfer regime, maximum heat transfer rate is achieved by placing the heat source close to the corners of the cavity; while, for Ra = 106, positioning the heat source near the middle of the cavity''s bottom wall yields the maximum average Nusselt number. Moreover, it is observed that the average Nusselt number is generally an increasing function of the volume fraction of the nanoparticles.

The bio-synthesis of nanomaterials is emerging as an innovative methodology, which is comparatively eco-friendly and inexpensive. Among di erent microbes, the role of fungi has been proved considerably promising in the in-vitro synthesis of nanomaterials. In this study, the comparative ecacy of four di erent species of Aspergillus (A. fumigatus, A. niger, A. avus and A. terreus) was investigated for the synthesis of silver nanoparticles (AgNPs). Initially, the synthesis was monitored through changes in coloration (yellow to dark brown) of the reaction solution containing AgNO3 reacted with the fungal biomass, of each fungi for 96 hours (hr) at 28C. The UV-visible spectra of the reaction mixture taken at di erent times showed a gradual change in absorbance between 400-420 nm, corresponding to changes in the surface plasmon resonance of the Ag metal. Comparatively, A. fumigatus showed a higher rate of nanoparticle synthesis than the other fungi. X-Ray Di raction (XRD) spectra showed peaks of various intensities, with respect to the angle of di raction (2), thus, revealing the crystalline nature of AgNPs. Nanoparticles fabricated through A. fumigatus (5-18 nm) and A. avus (13-26 nm) exhibited more drift towards monodispersity, which was relatively higher (6-70 nm) than in the other two fungi. Transmission Electron Microscopy (TEM) further con rmed the con guration of AgNPs in the range of 3-80 nm.

A new, simple, fast and reliable procedure for the speciation of selenium(IV) and selenium(VI) using Solid-Phase Extraction (SPE) with ammonium pyrrolidine dithiocarbamate/ sodium dodecyl sulfate immobilized on alumina-coated magnetite nanoparticles (APDC/SDS-ACMNPs), followed by electrothermal atomic absorption measurement, is proposed. The method is based on the adsorption of Se(IV) on modi ed ACMNPs. Total selenium concentration in di erent samples was determined as Se(IV), after reduction of Se(IV) to Se(VI), by heating the samples in a microwave oven with 4.0 mol L1 HCl. Se(VI) concentration was calculated as the di erence between the total selenium content and Se(IV) content. The e ect of parameters such as pH, amount of adsorbent, contact time, sample volume, eluent type, and HCl and APDC/SDS concentration ratios as modi ers, on the quantitative recovery of Se(IV), was investigated. Under optimal experimental conditions, the preconcentration factor, detection limit, linear range and Relative Standard Deviation (RSD) of Se(IV) were 125 (for 250 mL of sample solution), 0.05 ng mL1, 0.1- 8.0 ng mL1 and 4.1% (for 5.0 ng mL1; n = 7), respectively. This method avoided the time-consuming column-passing process of loading large volume samples in traditional SPE through the rapid isolation of APDC/SDS-ACMNPs with an adscititious magnet. The proposed method was successfully applied to the determination and speciation of selenium in di erent water samples and suitable recoveries were obtained.

Herein, we report a simple approach for increasing the photothermalconversion efficiency of gold rods (GRs) as a result of between gold rod and graphene oxideFor preparation of these hybrid materials, gold rods were synthesized and modified using functionalized polyethylene glycol-triazine (PEG-T). Then functionalized gold rods (GR-P) were attached to grapheneoxide (GO) sheets by π-π stacking. It was found that GR-P coating can improve the stability of GO in aqueous solutions. Moreovercellular experiments showed that GR-P coating on GO induce remarkably reduced cell toxicity. Gold rod-graphene oxide (GR-P-GO) hybrid materials hold great promise for application in various biomedical fields such as photothermal cancer therapy.

Nano inverse emulsion polymerization has been used to synthesize high molecular weight polyacrylamide nanoparticle with hydrophobic nanoscale coating layer with low molecular weight. These core-shell nanoparticles modify the polymer flooding process which can eliminate almost all problems of classical polymer flooding such as polymer solution high viscosity, polymer absorption and mechanical, thermal and biological degradations of the polymer. The nanostructure was characterized by dynamic light scattering (DLS) particle size analysis, thermal analysis (DSC), and UV-Vis spectroscopy that confirm a core-shell nanostructure for produced particles with considerable interaction of two polymers with narrow size distribution (90-140 nm). Also, micromodel and solubility experiments show that this method could enhance considerably performance of the classical polymer flooding and reduce polymer usage during the polymer flooding process.

We have studied the dynamical polarizability associated to energy loss spectra of armchair carbon nanotubes in the context of tight binding model Hamiltonian including long range electronic interaction. Linear response theory in the context of random phase approximation has been implemented to obtain charge response function via calculating correlation function of density operators. The effects of both temperature and electron doping as well as the diameter on the frequency behaviour of charge response have been investigated. The sharp peak in the energy loss spectra of the armchair carbon nanotube disappears upon raising the temperature. This is not the case of non interacting case where temperature has no considerable effect on the dynamical susceptibility. Also, the similar calculations have been performed for graphene sheet.

Pull-in instability of Boron Nitride Nano-Beam (BNNB) under the combined electrostatic and Casimir force as nano-switch is presented. Using Euler-Bernoulli Beam (EBB) theory, nonlocal piezoelasticity theory, von Karman geometric nonlinearity and virtual work principle, the nonlinear governing di erential equations are obtained. The equations are discretized by two types of numerical methods, namely the Modi ed Adomian Decomposition (MAD) method and Di erential Quadrature Method (DQM). Analysis of lower pull-in voltage values is considered for nano-switches with di erent boundary conditions. The detailed parametric study is considered, focusing on the remarkable eff ects of nonlocal parameter, beam length, boundary condition, geometrical aspect ratio and gap distance on the behavior of the pull-in instability voltage. The obtained results of DQM and MAD are compared with published relevant study. This work is hoped to be useful in designing and manufacturing of Nano-Electro-Mechanical Systems (NEMS) in advanced applications such as high-tech devices and nano-transistors with great applications in computer industry.

In the present study, the frequency response of skew and trapezoidal shaped single layer graphene sheets are studied via Kirchho plate theory. A four node Discrete Singular Convolution (DSC) method is developed for free vibration analysis of arbitrary straight-sided quadrilateral graphene. The straight-sided skew and trapezoidal graphene is mapped into a square graphene in the computational space using a four-node element. By using the geometric transformation, the governing equations and boundary conditionsof the graphene are transformed from hte physical domain into a square computational domain. Numerical examples illustrating the accuracy and convergence of the DSC method for skew and trapezoidal shaped graphene sheets are presented. New results for skew and trapezoidal shaped graphene have been presented, which can serve as benchmark solutions for future investigations.