Sharif Digital Repository

Liquid storage tanks are essential structures that are often located in residential and industrial areas; thus an assessment of their seismic performance is an important engineering issue. In this paper, the seismic response of unanchored steel liquid storage tanks is investigated using the endurance time (ET) dynamic analysis procedure and compared to responses obtained for anchored tanks under actual ground motions and intensifying ET records. In most cases, the results from ground motions are properly obtained with negligible differences using ET records. It is observed that uplifting of the tank base, which is closely related to the tank aspect ratio, has the greatest significance in the... 

Reinforcement of styrene-butadiene-rubber (SBR) was investigated using two different carbon blacks (CBs) with similar particle sizes, including highly structured CB and conventional CB, as well as multi-walled carbon nanotube (MWCNT) prepared by mechanical mixing. The attempts were made to examine reinforcing mechanism of these two different classes of carbon nanoparticles. Scanning electron microscopy and electrical conductivity measurement were used to investigate morphology. Tensile, cyclic tensile and stress relaxation analyses were performed. A modified Halpin-Tsai model based on the concept of an equivalent composite particle, consisting of rubber bound, occluded rubber and... 

Cadmium sulfide (CdS) with different morphologies was successfully prepared by solvothermal process by controlling the processing parameters, including nature of precursor and solvent, reaction temperature and process time. X-ray diffraction patterns revealed that, in all cases highly pure and crystallized CdS with hexagonal structure were obtained. In addition, it was found that the processing parameters influence on preferable growth direction of CdS nanostructures. Field emission scanning electron microscope analysis showed that CdS nanowires with different aspect ratios were obtained (depending upon the reaction temperature and process time) in presence of sulfur powder and... 

Extensive wind tunnel tests were performed on several wing- body-tail combinations in subsonic flow to study the effects of wing geometric parameters on the flow field over the tail. For each configuration, tail surface pressure distribution, as well as the velocity contour at a plane perpendicular to the flow direction behind the wing was measured. The results show a strong effect of wing to tail span ratio, as well as wing aspect ratio, on the flowfield downstream of the wing. For low sweep wings, as those considered here, wing and body interference effects on the tail are associated with the wing tip vortex and nose-body vortex  

During the recent decade, high induction diffusers have become more appealing in applications which require relatively high ventilation airflow rates, such as clean rooms. In this research, the effect of geometric parameters on the performance of a specific type of swirling air diffuser is investigated numerically. The results show that although the diffuser slots geometry, namely their angle and aspect ratio, is impressive on the diffuser performance, it is not as important as the swirling blade angle and the performance is almost constant in a wide range of slots specifications. The results also demonstrate that the diffuser performance and the resultant indoor airflow distribution highly... 

Cadmium sulfide (CdS) nanowires and nanorods with different aspect ratios were successfully synthesized by the solvothermal method aided with various solvents, namely ethylenediamine, ethanolamine and triethylene tetraamine. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses revealed that, highly pure CdS nanostructures were crystallized with different structures and preferable growth orientations depending on solvent nature. Field emission electron microscope (FE-SEM) images showed that the aspect ratio of CdS nanostructures depends upon the dielectric constant and boiling temperature of solvents. CdS nanostructures with the highest aspect ratio in the form... 

Nanostructured AA6063 (NS-Al) powder with an average grain size of ~100. nm was synthesized by high-energy attrition milling of gas-atomized AA6063 powder followed by hot extrusion. The microstructural features of the consolidated specimen were studied by transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) techniques and compared with those of coarse-grained AA6063 (CG-Al) produced by hot powder extrusion of gas-atomized powder (without using mechanical milling). The consolidated NS-Al alloy consisted of elongated ultrafine grains (aspect ratio of ~2.9) and equiaxed nanostructured grains. A high fraction (~78%) of high-angle grain boundaries with average... 

In this article a simple penetration model for the terminal ballistic of long rod penetrators is developed. The model is to predict the crater depth of a projectile penetrating into a semi-infinite target. A principle objective was to take an account of strength properties of colliding materials using erosive phenomena. The entire velocity regime from low to hypervelocity is analysed. The effect of the penetrator aspect ratio is also considered in the model. The model developed here is based on the steady-state penetration process and is used to compare with existing experimental measurements. The results of the comparison show very good agreement with experimental investigations of other... 

Nanocomposite films based on low density polyethylene (LDPE), containing of 2, 3, and 4. wt.% organoclay (OC) and ethylene vinyl acetate (EVA) copolymer as a new compatibilizer were prepared and characterized using rheological tests, X-ray diffraction, differential scanning calorimetry, oxygen permeation measurements, and tensile tests. There was no exfoliation or intercalation of the clay layers in the absence of EVA, while an obvious increase in d-spacing was observed when the samples were prepared with EVA present. This issue was reflected in the properties of nanocomposites. The oxygen barrier properties of the LDPE/EVA/OC film were significantly better than those of the LDPE/OC film.... 

The objective of the present study is to predict Young's modulus of polymer-layered silicate nanocomposites (PLSNs) containing fully intercalated structures. The particular contribution of this article is to consider the changes in structural parameters of different intercalated morphologies in vicinity of each other. These parameters include aspect ratio of intercalated stacks, number of silicate layers per stack, d-spacing between the layers, modulus of the gallery phase, and volume fraction of each intercalated morphology. To do this, the effective particle concept has been employed and combined with the Mori-Tanaka micromechanical model. It has been shown that the simultaneous effects of... 

This article is focused on a simple approach for determining the natural frequency and mode shape of laminated angle-ply plates with various shapes by rectangular orthotropy. Since the boundary of the domain for all shapes are not natural to the material coordinate axes it seems appropriate to express the plate displacement amplitude in terms of a polynomial and a general shape function multiplication in the x and y coordinates. The boundary conditions considered are clamped and simply supported edges. The effect of the fiber orientation, layer number, and lamination sequence on the natural frequencies of plates is also considered. The natural frequency determinant has been generated using... 

In this study, the homotopy analysis method (HAM) is used to obtain an approximate analytical solution for geometrically non-linear vibrations of thin laminated composite plates resting on non-linear elastic foundations. Geometric non-linearity is considered using von Karman's straindisplacement relations. Then, the effects of the initial deflection, ply properties, aspect ratio of the plate and foundation parameters on the non-linear free vibration is studied. Comparison between the obtained results and those available in the literature demonstrates the potential of HAM for the analysis of such vibration problems, whose governing differential equations include the quadratic and cubic... 

Longitudinal ventilation is a common technique for smoke management during a fire accident within tunnels. In this paper, fire and smoke movement behaviour in longitudinally ventilated tunnels is investigated focusing on critical ventilation velocity. Firstly, critical velocity (VC) is evaluated for different heat release rates and results are compared and verified with model scale experimental data. Secondly, two fire scenarios inside tunnels with different cross sections are arranged and the reliability of some existing correlations for VC is explored. Results illustrate that using a combined geometric scale rather than the traditional single length-scale ones results in better estimation... 

Both nonlinear rheology and finite EDL thickness effects on the mixing process in an electroosmotically actuated Y-sensor are being investigated in this paper, utilizing a depthwise averaging method based on the Taylor dispersion theory. The fluid rheological behavior is assumed to obey the power-law viscosity model. Analytical solutions are obtained assuming a large channel width to depth ratio for which a 1-D profile can efficiently describe the velocity distribution. Full numerical simulations are also performed to determine the applicability range of the analytical model, revealing that it is able to provide accurate results for channel aspect ratios of ten and higher and quite... 

This paper is focused on presenting an accurate framework to describe frequency-dependent energy harvesting via magnetic shape memory alloys (MSMAs). Modeling strategy incorporates the phenomenological constitutive model developed formerly together with the magnetic diffusion equation. A hyperbolic hardening function is employed to define reorientation-induced strain hardening in the material, and the diffusion equation is used to add dynamic effects to the model. The MSMA prismatic specimen is surrounded by a pickup coil, and the induced voltage during martensite-variant reorientation is investigated with the help of Faraday's law of magnetic field induction. It has been shown that, in... 

In this paper, n-tier methodology is developed to design multilevel interconnect architecture of macrocells using single-wall carbon nanotube (SWCNT) bundles. Upper limit of low-bias voltage of SWCNT bundle interconnects is derived and its dependence on temperature, SWCNTs' diameter, and interconnect length is studied. Possibility of using SWCNT bundles as local interconnects at 7.5-nm technology node is discussed, and it is shown that SWCNT bundles with 1 nm diameter cannot be used at the first interconnect metal level. Using Cu and SWCNT bundles, multilevel interconnect architecture of a 7.5-nm ASIC macrocell is designed which reduces the number of metal levels by 27% and power dissipation... 

In this paper, we present a simple platform for colorimetric detection of glutathione using gold nanorods (AR ∼ 6.5 ± 0.2) as a plasmonic sensor. The functional mechanism of the sensor is based on shifts of longitudinal plasmon resonance during selective transverse overgrowth induced by preferential binding of glutathione at the nanorod tips. Under the optimum conditions, a calibration curve showed two linear regimes at the range of 50 nM to 20 μM of glutathione with a detection limit as low as 40 nM. The nanosensor maintains relatively high selectivity for determination of glutathione in the presence of several other amino acids. However, cysteine at similar concentration levels strongly... 

The electrokinetic phenomena at high zeta potentials may show several unique features which are not normally observed. One of these features is the ionic size (steric) effect associated with the solutions of high ionic concentration. In the present work, attention is given to the influences of finite ionic size on the cross stream diffusion process in an electrokinetically actuated Y-shaped micromixer. The method consists of a finite difference based numerical approach for non-uniform grid which is applied to the dimensionless form of the governing equations, including the modified Poisson-Boltzmann equation. The results reveal that, neglecting the ionic size at high zeta potentials gives... 

A continuum theory is employed to numerically study the equilibrium orientation and defect structures of a circular cylindrical particle with flat ends under a homeotropic anchoring condition in a uniform nematic medium. Different aspect ratios of this colloidal geometry from thin discotic to long rodlike shapes and several colloidal length scales ranging from mesoscale to nanoscale are investigated. We show that the equilibrium state of this colloidal geometry is sensitive to the two geometrical parameters: aspect ratio and length scale of the particle. For a large enough mesoscopic particle, there is a specific asymptotic equilibrium angle associated to each aspect ratio. Upon reducing the... 

The process of imaging a biomolecule by atomic force microscope (AFM) is modeled using molecular dynamics (MD) simulations. Since the large normal force exerted by the tip on the biosample in contact and tapping modes may damage the sample structure and produce irreversible deformation, the noncontact mode of AFM (NC-AFM) is employed as the operating mode. The biosample is scanned using a carbon nanotube (CNT) as the AFM probe. CNTs because of their small diameter, high aspect ratio and high mechanical resistance attract many attentions for imaging purposes. The tip-sample interaction is simulated by the MD method. The protein, which has been considered as the biomolecule, is ubiquitin and a...