Sharif Digital Repository

Propagation of the torsional surface waves in a medium consisting of a functionally graded (FG) substrate bonded to a thin piezoelectric over-layer has been analytically formulated in the mathematical framework of surface/interface elasticity theory. In the cases where the wavelength and/or the thickness of the over-layer are comparable to the surface/interface characteristic length, then the surface/interface effects are not negligible. It is assumed that the over-layer is made of hexagonal 622 crystals with a single axis of rotational symmetry coinciding with the axis of polarization. The half-space is made of an FG transversely isotropic material in which the elasticity tensor and the... 

In this study, we numerically determined the performance of a microscale separator comprising a lateral and a main channel to separate a two-phase flow. It was aimed to conduct continuous phase through the lateral channel and dispersed phase through the main channel. The continuous and dispersed phases were modeled as incompressible Newtonian fluids with the corresponding interface tracked by the phase-field model. The dynamics, including pressure fluctuations in the separator, were further examined. It was mechanistically demonstrated how the geometry of the separator modulates the phase separation. Further examined were the influences of various geometrical parameters on the performance of... 

Design and operation of an opto-mechanical system for spectral analysis using a double fiber design for light delivery are reported in this study. A simple mechanical drive system is used, which is able to perform a fine course of angular motion for the scanning of the dispersive optical element. The presented system consists of a mechanical drive system, a dispersive element, a double fiber assembly and a photodetector. A source light, a digital multimeter and a PC are used to test the presented design. The first-order diffraction of the white light source is obtained by using a reflection diffraction grating in Littrow arrangement. By comparing the output reflection signals of the plane... 

A novel technique for upscaling of detailed geological reservoir descriptions is presented. The technique aims at reducing both numerical dispersion and homogenization error, generated due to incorporating a coarse computational grid and assigning effective permeability to coarse grid blocks respectively. In particular we consider implicit-pressure explicit-saturation (IMPES) scheme where homogenization error impacts the accuracy of the coarse grid solution of the pressure equation. To reduce the homogenization error, we employ the new vorticity-based gridding that generates a non-uniform coarse grid with high resolution at high vorticity zones. In addition, to control numerical dispersion,... 

Graphene nanoplatelets (GNPs) are ideal reinforcements for improving the mechanical properties of aluminum-based matrices due to their outstanding properties. However, it essentially depends on their uniform dispersion in the matrix. In this study, the challenge of uniform dispersion of graphene was performed by functionalizing the non-covalent surface and sonication of GNPs applying non-ionic polymeric ethyl cellulose (EC) surfactant, in which a colloidal mixture was provided with Al powder and graphene, followed by sintering at 620 °C and consolidation. The density and mechanical properties of nanocomposite specimens were investigated and compared with a non-surfactant-assisted Al/GNP... 

A simple analytic formula is derived to extract tiny dispersion fluctuations along highly nonlinear fibers from distributed measurements of parametric gain. A refined BOTDA scheme, suitable to track Kerr processes, enables low noise measurements  

Monodisperse closed cell aluminum foam was analyzed numerically to determine the relationship between its elastic modulus, porosity and pore diameter. It was found a nonlinear relationship exists between porosity, pore diameter and modulus of elasticity. In this regard, an empirical equation is developed and implemented for the prediction of modulus of elasticity versus porosity and pore diameter. Comparing experimental and analytical approaches by other researchers with those obtained in this research shows agreement exists within 1 to 3 percent  

Numerical and analytical exact solutions of diffusional release from a cylindrical polymeric matrix into an infinite medium have been developed in which the initial solute loading (A) is greater than solubility limit (Cs). Also, the effects of boundary layers on the drug release rate have been studied. The numerical solution is valid for any initial drug loading whereas analytical solution can be used for high values of drug loading. Comparisons have been made between numerical and analytical exact solutions in upper and lower bounds (A/Cs蠑1 and A/Cs→1) and previously presented approximate solution. The presented results validate the proposed numerical solution  

Different grades of carbon nanotubes (CNTs) were dispersed in poly(tetramethylene ether glycol) (PTMEG) without any solvent in the presence of a block copolymer dispersing agent by ultrasonication at a temperature well above the melting point of the PTMEG. The state of CNT dispersion at different length scales was evaluated by using optical microscopy, UV-Vis spectroscopy, rheological measurements, differential scanning calorimetry, thermogravimetric analysis and sedimentation tests. Optical microscopy can be used to characterize the state of dispersion and CNT network formation on a micrometer scale, whereas UV-Vis provides useful information about the dispersion of individual CNTs at... 

Finite impulse response (FIR) and infinite impulse response (IIR) digital filters are proposed to allow for time-domain simulation of optical pulse propagation by using the operator-splitting technique. These filters simulate polarization mode dispersion and chromatic dispersion effects with acceptable accuracy in time-domain. An analytical relation between the coefficients of these filters and the simulation step-size is established to accommodate the possibility of carrying out the time-domain split-step method with variable split-step length at virtually no computational burden. The superiority of the proposed method over the conventional frequency-domain technique is particularly... 

An elliptic micro-/nano-obstacle bonded to an infinite body incident upon by SH-waves, where both domains are couple stress media with micro-inertia, is of major concern. The formulation of this problem in the mathematical framework of couple stress elasticity with micro-inertia leads to angular and radial Mathieu differential equations which are solved analytically. These equations carry two characteristic lengths which are peculiar to the discrete nature of each domain enabling the capture of size effect, dispersion phenomenon, as well as the enhancement of the accuracy of the results. For verification, the ratio of the semi-axis of the elliptic obstacle is set equal to 1, and the result... 

Wettability alteration analysis form gas-repellent to gas-wet with the aid of chemical agents has been subjected of numerous studies. However, fundamental understanding of the effect of surface tension of liquid on repellency strength, the change in the intermolecular forces due to the adsorption of nanoparticles onto the rock surfaces, and exposure of treated rock in brine are not well discussed in the available literature. In this study, X-ray diffraction, Atomic Force Microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were applied to characterize the treated and fresh samples. Dynamic and static contact angle measurements were then combined with six methods... 

A model based on the perturbation theory of fluids was proposed to correlate the experimental data for surface tension of pure hydrocarbons in a wide range of temperature. The results obtained for the pure hydrocarbons were directly used to predict the surface tension for binary hydrocarbon mixtures at various temperatures. In the proposed model, a modified form of the square well potential energy between the molecules of the reference fluid was taken into account while the Lennard-Jones dispersion energy was considered to be dominant amongst the molecules as the perturbed term to the reference part of the model. In general, the proposed model has three adjustable parameters which are chain... 

In the present study, an analytical strategy was developed using reduced graphene oxide (rGO) as an effective sorbent in dispersive micro-solid phase extraction (DMSPE) for simultaneous determination of seven polycyclic aromatic hydrocarbons (PAHs) combined with gas chromatography (GC-FID). rGO was synthesized using modified Hummer's method and characterized using scanning electron microscope (SEM), atomic force microscope (AFM) and Raman spectroscopy. A rotatable central composite design (CCD) combined with multiple linear regression (MLR) and analysis of variance (ANOVA) was used for designing, modelling and optimization of the extraction procedure. In this regard, principal component... 

A stable porous zinc-based metal organic framework (MOF) containing nitrogen-rich bis-tetrazolate ligand was synthesized to study the role of similar structures concerning both extractive phase and the desired solutes to achieve greater sorption efficiency. With implementing a dispersive micro-solid phase extraction (d-µ-SPE) methodology, the sorption capability and influencing structural parameters i.e., porosity, surface area and interactions types were investigated for the synthesized zinc-bis-tetrazolate (ZnBT) MOF and compared with some synthesized sorbents such as MIL-101, MIL-101-NH2, cadmium naphthalene dicarboxylic acid dimethyl formamide [Cd(NDC)(DMF)], polyaniline and LiChrolut®...