Sharif Digital Repository

Gold nanoparticles are widely used as high efficient photon-thermal energy converters in a broad range of applications. This paper presents a theoretical investigation on using the optothermal properties of gold nanoparticle arrays to generate nanoscale molten and rubbery regions on the surface of an amorphous polymeric film. Nanoparticles are assumed to be embedded in a transparent silica layer and illuminated with a 7.5 ns pulsed laser at 532 nm. Simulation results are presented for systems with single gold nanoparticles, dimers and chains. Both electromagnetic and thermal interaction between nanoparticles are found to be important factors in determining the result of surface processing.... 

A simple chemisorption method was used to graft on the surface of MWCNTs and Graphene nanoparticles to prepare stable kerosene-based MWCNTs and Graphene nanofluids. The prepared nanofluids remained stable for more than five months and no sedimentation was observed. Regarding the effect of temperature on thermo-physical properties, it was observed that although increasing nanoparticle concentration led to an increase in the fluid viscosity, it was negligible enough at lower nanoparticle loading. Moreover, adding nanoparticles to the base fluid did not have any noticeable impact on the fluid density which was negligible even at high concentrations. The thermal conductivity improvement was... 

Wax deposition inside pipelines is a major concern in oil and gas industries, and it must be continuously monitored. In this paper, a mathematical-experimental combined method based on the Compton scattering was proposed to determine the thickness of the wax deposited inside the industrial pipes. For this purpose, first, the relationship between the intensity of the backscattered gamma-rays and the thickness of the wax inside the pipe was mathematically modeled. Then, an experimental setup was prepared for measuring the intensity of the backscattered gamma-rays from the pipes with different wall thicknesses and different wax widths. Finally, the experimentally measured counts were used by... 

Optical fiber doped with lead salts quantum dots (QDs) of different radii, has previously been proposed as a wide-band amplifier in the optical communication range. The emission and absorption spectra of QDs are size-dependent. Optical fiber amplifier doped with QDs of different sizes is an inhomogeneous gain medium. This inhomogeneity is the principle of operation of wide-band quantum-dot-doped fiber amplifiers (QDFAs). To study the effects of inhomogeneity such as spectral hole burning on the amplifier behavior, a fiber amplifier with an arbitrary size distribution of QDs is taken into consideration. The light propagation equations and rate equations for the inhomogeneous medium are... 

The aim of this study is to determine the determine effects of magnesium supplementation on anthropometric indices Consist of body weight (BW), waist circumference (WC), body mass index (BMI) and body fat percentage (BF%). In this systematic review and dose-response meta-analysis, we searched PubMed, Cochrane Library, Scopus, Web of Science and Google Scholar from databases inception up February 2020 for relevant randomized controlled trials. Quality of evidence was evaluated using the Cochrane Collaboration Tool. All of outcome in this meta-analysis were pooled using Random Effect Model. Analysis of dose-response for magnesium dosage was carried out using a fractional polynomial model. The... 

Abstract The aim of this study was to determine the effects of Mg supplementation on anthropometric indices consisting of body weight, waist circumference (WC), BMI and body fat percentage. In this systematic review and dose-response meta-analysis, we searched PubMed, Cochrane Library, Scopus, Web of Science and Google Scholar from databases inception up to February 2020 for relevant randomised controlled trials. Quality of evidence was evaluated using the Cochrane Collaboration Tool. All the outcomes of this meta-analysis were pooled using the random effect model. Analysis of dose-response for Mg dosage was carried out using a fractional polynomial model. The systematic review and... 

In this paper, a novel approach is proposed for solving the nonlinear problems based on the collocation and energy balance methods (EBMs). Rational approximation is employed as an initial guess and then it is combined with EBM and collocation method for solving nonlinear oscillators with cubic term. Obtained frequency amplitude relationship is compared with exact numerical solution and subsequently, a very excellent accuracy will be revealed. According to the numerical comparisons, this method provides high accuracy with 0.03% relative error for Duffing equation with strong nonlinearity in the second-order of approximation. Furthermore, achieved results are compared with other types of... 

This paper introduces a tunable design for an electrically actuated vibrating ring micro-gyroscope. This mechanism contains eight piezoelectric micro-beams attached to the vibrating ring in each drive and sense directions. Employing a full geometric non-linear model for the vibrating ring and accounting for the micro-beam’s mid-plane stretching; the mathematical model associated with the present system is obtained. Afterward, utilizing the Hamilton principle together with the Ritz method, the reduced equations of motion are derived. The present results are validated by those available in the literature for simpler systems. A three-dimensional (3D) finite element (FE) simulation was carried... 

This paper introduces a tunable design for an electrically actuated vibrating ring micro-gyroscope. This mechanism contains eight piezoelectric micro-beams attached to the vibrating ring in each drive and sense directions. Employing a full geometric non-linear model for the vibrating ring and accounting for the micro-beam’s mid-plane stretching; the mathematical model associated with the present system is obtained. Afterward, utilizing the Hamilton principle together with the Ritz method, the reduced equations of motion are derived. The present results are validated by those available in the literature for simpler systems. A three-dimensional (3D) finite element (FE) simulation was carried... 

We theoretically investigate entanglement in a hybrid quantum system comprising two optical cavities coupled to a shared microwave cavity via optomechanical interactions. Our results demonstrate that increasing the microwave input power and frequency in the allowed range enhances entanglement between the microwave–optical and optical–optical modes. We also show by change frequency of the one optical cavity in the communication domain that we still have entanglement. This ability to generate robust microwave–optical photon entanglement shows promise for various quantum technologies. Optical photons could enable secure quantum communication in optical fibers, while microwave photons allow... 

Splashing in the Peirce Smith copper converter was investigated using the Smoothed Particle Hydrodynamics (SPH) method. A model 50 cm in diameter (one eighth of the actual convertor) was made to verify results. The ffect of air flow rate and the distance of air blowers from the surface were identified as two major contributors to splashing and their effect on splashing was investigated. Using C++ based on SPH method, a model, geometrically identical to the physical model, was designed for simulation and verification of results. It was found that splashing may be reduced by as much as 85% by controlling the air flow rate into the convertor  

In this article an analytical solution is presented for power output from a piezoelectric shallow shell energy harvester using higher order shear deformation theory (HSDT). The energy harvester is made of an elastic substrate layer coupled with one or two surface bonded piezoelectric layers. Mechanical equations of motion with Gauss's equation are derived on the basis of HSDT and solved simultaneously for simply-supported mechanical boundary conditions. The electromechanical frequency response functions that relate the power output and circuit load resistance are identified from the exact solutions. Using Rayleigh damping the influence of structural damping is taken into account. Also... 

In this paper, the well-known effective medium approximation (EMA) and coupled dipole approximation (CDA) methods are employed to study the optical properties of a metal nanoparticle-block copolymer (MNP-BCP) nanocomposite. This approach is applied to study a system consisting of small gold spherical nanoparticles randomly distributed in the cylindrical micelles of a di-BCP. At first, the EMA method is used to obtain the effective dielectric function of a semi-metallic cylinder. Then, the extinction spectrum of the hexagonal 2D-array of semi-metallic cylinders is obtained by the CDA method. This procedure makes it possible to study simultaneously both the electromagnetic extinction of MNPs... 

In this study, H4Ti5O12 nanotubes have been prepared as Li+ adsorbent by acid treatment of Li4Ti5O12 nanotubes. Li4Ti5O12 nanotubes were synthesized via a hydrothermal method in which TiO2(B) nanNotubes were used as a precursor. The prepared Li-ion sieve showed a significant high ion-exchange capacity (160.6 mgg-1) for lithium ions due to its large specific surface area of 115.4 m2 g-1 compared to the other related studies. The kinetics and isotherm investigation revealed that the pseudo-second-order equation well described the adsorption kinetics, and the Langmuir model well fitted the isotherm data. Furthermore, the low value of adsorption energy obtained from the Dubinin-Radushkevitch... 

In this study, H4Ti5O12 nanotubes have been prepared as Li+ adsorbent by acid treatment of Li4Ti5O12 nanotubes. Li4Ti5O12 nanotubes were synthesized via a hydrothermal method in which TiO2(B) nanNotubes were used as a precursor. The prepared Li-ion sieve showed a significant high ion-exchange capacity (160.6 mgg−1) for lithium ions due to its large specific surface area of 115.4 m2 g-1 compared to the other related studies. The kinetics and isotherm investigation revealed that the pseudo-second-order equation well described the adsorption kinetics, and the Langmuir model well fitted the isotherm data. Furthermore, the low value of adsorption energy obtained from the Dubinin-Radushkevitch... 

In this work, we attempted to develop an Implicit Coupled Density-Based (ICDB) solver using LU-SGS algorithm based on the AUSM+ up scheme in OpenFOAM. Then sonicFoam solver was modified to include viscous dissipation in order to improve its capability to capture shock wave and aerothermal variables. The details of the ICDB solver as well as key implementation details of the viscous dissipation to energy equation were introduced. Finally, two benchmark tests of hypersonic airflow over a flat plate and a 2-D cylinder were simulated to show the accuracy of ICDB solver. To verify and validate the ICDB solver, the obtained results were compared with other published experimental data. It was... 

The aim of this paper is to use higher-order energy balance method as a novel solution procedure for investigation the nonlinear oscillation of various systems. The method is associated with collocation method and employed for a group of nonlinear problems including pure cubic nonlinearity, fractional elastic force and duffing harmonic terms. Obtained results are evaluated by comparing with the classical balance method and also the exact solutions computed numerically. It is shown our solution procedure achieves more accurate results versus the classical solution and higher agreement are observed between the newer solutions and the exact ones for the systems. Effect of initial conditions in... 

This article presents a model to simulate the behavior of a magnetic shape memory alloy while harvesting vibratory energy. In this type of energy harvester, magnetic shape memory alloy element is placed in the air gap of a ferromagnetic core which conducts the magnetic flux. Two apparent coils are wound around a ferromagnetic core: one to produce bias magnetic field by passing a rectified electric current and the other to serve as an energy pickup coil. Applying compressive time-variant strain field to magnetic shape memory alloy element changes its dimensions and magnetic properties as well. Presence of the bias magnetic field returns magnetic shape memory alloy element to its initial state... 

The effects of geometrical scaling on a supersonic external compression axisymmetric inlet are investigated. Various lower and higher geometrical scales of supersonic inlet are considered as the case studies. The inlet flow is simulated numerically using RANS solver along with the SST k-w turbulence model. The numerical results are in an acceptable agreement with the NACA experimental data at free stream Mach number of 1.79 and at zero angle of attack. The results show that the static pressure distribution of the inlet flow experiences some differences for various scales especially at the regions of the flow entrance and throat area. The mean flow Mach number and the mass flow rate at the...