Sharif Digital Repository

Heart attack is one of the most common causes of death in the world. Coronary artery disease is the most recognized cause of heart attack whose onset and progression have been attributed to low-density lipoprotein (LDL) passing through the wall of the artery. In this paper, hemodynamic variables as well as the concentration of LDL through the coronary porous artery at the Left Anterior Descending coronary artery (LAD), and its first diagonal branch (D1) under the heart motion investigated using computational simulation. The geometry that has been studied in this paper is the first bifurcation of Left Anterior Descending (LAD) that has been placed on a perimeter of hypothetical sphere... 

Recent experiments have shown the applicability of single-layer graphene sheets (SLGSs) as electromechanical resonators. Existing theoretical models, based on linear continuum or atomistic methods, are limited to the study of linear vibrations of SLGSs. Here we introduce a hybrid atomistic-structural element which is capable of modelling nonlinear behaviour of graphene sheets. This hybrid element is based on an empirical inter-atomic potential function and can model the nonlinear dynamic response of SLGSs. Using this element, nonlinear vibrational analysis of SLGSs is performed. It is shown that the nonlinear vibrational analysis of SLGSs predicts significantly higher fundamental... 

The nonlinear vibrational properties of single layer graphene sheets (SLGSs) are investigated using a membrane model. The nonlinear equation of motion is considered for the SLGSs by including the effects of stretching due to large amplitudes. The equation of motion is numerically solved utilizing the finite difference method for SLGSs with different initial and boundary conditions, sizes and pretensions. It is concluded that the nonlinear fundamental frequency of SLGSs increases by increasing the pretension and initial velocity. In addition, it is observed that an increase in the pretension weakens the effects of the initial velocity on the fundamental frequency, such that the fundamental... 

Molecular structural mechanics approach is implemented to investigate vibrational behavior of single-layered graphene sheets. By using the atomistic modeling, mode shapes and natural frequencies are obtained. Vibration analysis is performed under different chirality and boundary conditions. Numerical results from the finite element technique are applied to develop empirical equations via a statistical multiple nonlinear regression model. With the proposed empirical equations, fundamental frequencies of single-layered graphene sheets under considered boundary conditions can be predicted within 3 percent accuracy. Copyright © 2007 by ASME  

In this work, a new structure of single layer armchair graphene nanoribbon field effect transistor with the Stone–Wales (SW) defect (SWGNRFET) is studied. The simulations are solved with Poisson–Schrödinger equation self-consistently by using Non-Equilibrium Green Function (NEGF) and in the real space approach. The energy band structure is obtained by approximation tight-binding method. The results show that displacement of a defect in the width of the channel of the new structure is led to 50% increase in ION/IOFF ratio only by rotating of a C–C (Carbon–Carbon) bond with similar behavior. But, a remarkable increase of 300% in ION/IOFF ratio is obtained by a “dual center” defect. The results... 

Within the elasticity formulation the most general displacement field for hygrothermal problems of long laminated composite plates is presented. The equivalent single-layer theories are then employed to determine the global deformation parameters appearing in the displacement fields of general cross-ply, symmetric, and antisymmetric angle-ply laminates under thermal and hygroscopic loadings. Reddy's layerwise theory is subsequently used to determine the local deformation parameters of various displacement fields. An elasticity solution is also developed in order to validate the efficiency and accuracy of the layerwise theory in predicting the interlaminar normal and shear stress... 

We present a new TiO2 morphology, featuring high surface area and open structure, synthesized by a two-step chemical route for the manufacture of dye-sensitized solar cells (DSSCs). This construct is sets of intertwined one-dimensional (1D) nanostructures (i.e., nanotubes), so-called skein-like nanotubes (NTs). Such morphology is produced by a combination of TiC oxidation and hydrothermal processes. The mesoporous TiO2 nanoparticles, as the product of TiC oxidation operation, is used as the precursor of hydrothermal process to grow the skein-like NTs. The effect of processing parameters of TiC oxidation and hydrothermal processes is studied. The skein-like morphology enables to eliminate the... 

Single-layer reduced graphene oxide nanoribbons (rGONRs) were obtained through an oxidative unzipping of multi-walled carbon nanotubes and a subsequent deoxygenation by hydrazine and bovine serum albumin. Human mesenchymal stem cells (hMSCs) were isolated from umbilical cord blood and used for checking the concentration- and time-dependent cyto- and geno-toxic effects of the rGONRs and reduced graphene oxide sheets (rGOSs). The cell viability assay indicated significant cytotoxic effects of 10 μg/mL rGONRs after 1 h exposure time, while the rGOSs exhibited the same cytotoxicity at concentration of 100 μg/mL after 96 h. The oxidative stress was found as the main mechanism involved in the... 

We investigate the possibility of frequency conversion in time-varying metasurfaces, composed of graphene microribbon arrays (GMRAs) with time-periodic modulation of their conductivity. We present a quasi-static model for the interaction of light with a temporally modulated metasurface, as well as an accurate analytical treatment of the problem of time-varying GMRAs. Results coming from numerical simulations are also available. We provide corrections to a previous related proposal for frequency conversion and refute the possibility of attaining frequency shifts not equal to an integral multiple of modulation frequency. Contrary to the preceding results, our findings show that efficient... 

In this paper, vibration analysis of rotating laminated composite cylindrical shells using a combination of the layerwise theory and wave propagation approach is investigated. This combination enables us to study all the conventional boundary conditions in our analysis. Results obtained have been compared with those available in the literature and a good agreement has been observed. In contrast to the Equivalent Single Layer theories (ESL), the layerwise theory is constructed on the basis ofC°- continuity through the laminate thickness. For the surface of the shell, a displacement field based on the wave propagation approach is proposed. The effect of Coriolis and centrifugal accelerations... 

Carbon nanostructures such as carbon nanotubes (CNTs) and graphene sheets have attracted great attention due to their exceptionally high strength and elastic strain. These extraordinary mechanical properties, however, can be affected by the presence of defects in their structures. When a material contains multiple defects, it is expected that the stress concentration of them superposes if the separation distances of the defects are low, which causes a more reduction of the strength. On the other hand, it is believed that if the defects are far enough such that their affected areas are distinct, their behavior is similar to a material with single defect. In this article, molecular dynamics... 

Lithium intercalation is a convenient method to prepare few-layer and single-layer MS2 (M=Mo, W) nanosheets. This method is, however, very time-consuming (few days) and it is difficult to control the reaction parameters. To overcome these drawbacks, we have proposed a method to use an Li battery set-up to significantly reduce the reaction time (few hours) and electrochemically intercalate lithium ions into MS2 layers in a controllable manner. Atomic force microscopy (AFM), scanning electron microscopy (SEM) and Raman spectroscopy results revealed that MoS2 and WS2 single-layer (thickness of ~ 1 nm) nanosheets with the 1T phase were prepared after intercalation in an Li battery set-up.... 

Lithium intercalation is a convenient method to prepare few-layer and single-layer MS2 (M=Mo, W) nanosheets. This method is, however, very time-consuming (few days) and it is difficult to control the reaction parameters. To overcome these drawbacks, we have proposed a method to use an Li battery set-up to significantly reduce the reaction time (few hours) and electrochemically intercalate lithium ions into MS2 layers in a controllable manner. Atomic force microscopy (AFM), scanning electron microscopy (SEM) and Raman spectroscopy results revealed that MoS2 and WS2 single-layer (thickness of ~ 1 nm) nanosheets with the 1T phase were prepared after intercalation in an Li battery set-up.... 

In the previous researches, several theoretical equations were presented for calculation of buildup factor of the single layer shields. Also, the theoretical equations were offered for the two-layered shield that consist of the known materials. For other possible modes of the multi-layered shield, the buildup factor are usually calculated via experimental or simulated data. The purpose of present study is the extraction of the new theoretical equation for the gamma ray buildup factor of three-layered spherical shield made of water, concrete and iron based on the Monte Carlo calculation. To this end, the gamma ray buildup factor of the three-layered spherical shield is calculated via... 

Although concrete armour units have traditionally been used in two layers, the application of single-layer armour has attracted more attention in recent years because of its lower concrete volume and faster construction pace. Single-layer amour relies mainly on the contact between units to provide stability; however, installation of special armour types with surface projections for better interlocking, increases the possibility of breakage. During the last decade the idea of using bulky armour units such as cubes has been raised, and the application of these single-layer armour units has become common for high-crested breakwaters. However, the application of cube armours for low-crested... 

In this study, a novel idea was utilized for designing high performance bilayer absorber for X-band frequency. The microwave dissipation features of the bilayer structure absorbers with one-layer bare resin epoxy and the other epoxy resin filled with [CaTiO3/ZnFe2O4]@C nanocomposite as lossy filler were simulated with CST studio suite within 2–18 GHz. The lossy filler was successfully developed via chemical method. In the first step two distinct single layer absorbers of bare resin epoxy and resin epoxy filled with [CaTiO3/ZnFe2O4]@C nanocomposite ([CT/ZF]@C) were prepared and in the second step the measured electromagnetic parameters were considered as input data of CST studio suite for... 

Herein, two distinct nanocomposites of CaTiO3 micro-cubes and polygonal SrFe12O19, both decorated with NiO nanoparticles, were successfully synthesized using hydrothermal method. The physico-chemical features of as-prepared samples were evaluated via XRD, FTIR, UV–vis, BET, XPS, FESEM and EDS analysis. Microwave attenuation features of as-prepared single layer absorbers were determined by VNA analysis in 2–18 GHz. Simulation confirmation was checked by preparing a bi-layer samples and evaluating it using VNA analysis after finding the appropriate thickness of each layer. The reflection loss from each single layer samples containing 20 wt% of each CaTiO3/NiO and SrFe12O19/NiO nanocomposites... 

Herein, two distinct nanocomposites of CaTiO3 micro-cubes and polygonal SrFe12O19, both decorated with NiO nanoparticles, were successfully synthesized using hydrothermal method. The physico-chemical features of as-prepared samples were evaluated via XRD, FTIR, UV–vis, BET, XPS, FESEM and EDS analysis. Microwave attenuation features of as-prepared single layer absorbers were determined by VNA analysis in 2–18 GHz. Simulation confirmation was checked by preparing a bi-layer samples and evaluating it using VNA analysis after finding the appropriate thickness of each layer. The reflection loss from each single layer samples containing 20 wt% of each CaTiO3/NiO and SrFe12O19/NiO nanocomposites... 

The present study is focused on the investigation of the absorption properties of the bi-layer absorber with different thickness and orientation approaches. Improvement in absorption exclusively depends on the various parameters as interfacial polarization, multiple reflections among layers, conduction loss, phase cancellations, and shape anisotropy, etc. By considering these parameters. Calcium titanate micro-cubes CaTiO3 (CTO) and polypyrrole nanotubes (PPy) nanocomposites were prepared and microwave absorption from single layer coaxial absorbers having M1 = CaTiO3+15 wt% polymer and M2 = CaTiO3+30 wt% polymer were determined. Different layer orientations and thicknesses of the bi-layer... 

One of the main subjects in automotive industries is to enhance the efficiency of internal combustion engines. Wear between cylinder and ring is one of the major parameters reducing the engine performance. So many parameters are affecting the wear losses. Temperature plays a key role on the severity of wear condition in internal combustion engines. In conventional cast iron cylinders, it is not possible to increase the temperature from a defined level, as it causes excessive wear in contact area between cylinder liner and piston ring. One of the major benefits of using ceramic coating is their ability to withstand in higher temperatures, while having adequate hardness to improve wear rate...