Thermo acoustic study of carbon nanotubes in near and far field: Theory, simulation, and experiment

, Article Journal of Applied Physics ; Volume 117, Issue 9 , 2015 ; 00218979 (ISSN) Asadzadeh, S. S ; Moosavi, A ; Huynh, C ; Saleki, O ; Sharif University of Technology

American Institute of Physics Inc 2015

Abstract

Carbon nanotube webs exhibit interesting properties when used as thermo-acoustic projectors. This work studies thermo-acoustic effect of these sound sources both in near and far field regions. Based on two alternative forms of the energy equation, we have developed a straightforward formula for calculation of pressure field, which is consistent with experimental data in far field. Also we have solved full 3-D governing equations using numerical methods. Our three-dimensional simulation and experimental data show pressure waves are highly affected by dimensions of sound sources in near field due to interference effects. However, generation of sound waves in far field is independent of...

Numerical Analysis of Underwater and Within Air Sound Generation by using Carbon Nanotube

, M.Sc. Thesis Sharif University of Technology Saleki, Omid (Author) ; Moosavi, Ali (Supervisor)

Abstract

Carbon nanotubes have special thermodynamic properties which makes suitable as a thermo-acoustic sound source. Recently it is shown that by using these nanotubes it is possible to generate strog sound waves in air or water. Experimental analysis of phenomenon can be complicated and expensive. Hence this fact, in this study using molecular dynamic simulation, numerical analysis of sound generation with CNTs in air and water is discussed. For this purpose, the required structue of the system is generated and it has reaced equilibrium. This process has been done for 6 diﬀerent CNT and for each CNT there are 5 diﬀerent distances between them. Althogether, 30 diﬀerent cases has is used for...

Investigation of Optical Bistability in Quantum Dot and Erbium Doped Fiber Ring Resonator

, M.Sc. Thesis Sharif University of Technology Saleki, Ziba (Author) ; Bahrampour, Alireza (Supervisor)

Abstract

Optical bistability is one of the most important results of nonlinear optics. The term optical bistability refers to the situation in which two different output intensities are possible for a given input intensity. Interest in optical bistability stems from its potential usefulness as a switch for use in optical communication and in optical computing. Optical bistability is resulted by nonlinear phenomena such as kerr effect, two photon absorption and saturable absorber. In this thesis, we study the optical bistability in a double-coupler ring resonator, in which the right half of ring is made of an erbium doped fiber amplifier for compensating the loss by the gain of EDFA, and the left half...

Molecular dynamics study of friction reduction of two-phase flows on surfaces using 3d hierarchical nanostructures

, Article Journal of Physical Chemistry C ; 2019 ; 19327447 (ISSN) Saleki, O ; Moosavi, A ; Kazemzadeh Hannani, S ; Sharif University of Technology

American Chemical Society 2019

Abstract

The use of superhydrophobic surfaces is one the most promising methods for reducing the friction and increasing the flow rate in fluid transfer systems. Because in such systems the surface structure plays a key role, in this study, we explore the performance of the hierarchical nanostructures. These nanostructures are inspired by the superhydrophobic surface of the lotus leaf. We consider a flow between two walls with hierarchical nanostructures and simulate the system via the molecular dynamics method. The size of the nanostructures and the distance between them have been studied to find whether a design with a maximum flow rate exists. The nanostructures have two parts, a bigger part on...

Molecular dynamics study of friction reduction of two-phase flows on surfaces using 3d hierarchical nanostructures

, Article Journal of Physical Chemistry C ; 2019 ; 19327447 (ISSN) Saleki, O ; Moosavi, A ; Hannani, S. K ; Sharif University of Technology

American Chemical Society 2019

Abstract

The use of superhydrophobic surfaces is one the most promising methods for reducing the friction and increasing the flow rate in fluid transfer systems. Because in such systems the surface structure plays a key role, in this study, we explore the performance of the hierarchical nanostructures. These nanostructures are inspired by the superhydrophobic surface of the lotus leaf. We consider a flow between two walls with hierarchical nanostructures and simulate the system via the molecular dynamics method. The size of the nanostructures and the distance between them have been studied to find whether a design with a maximum flow rate exists. The nanostructures have two parts, a bigger part on...

Friction reduction in a nanochannel with grafted poly(N-isopropylacrylamide) oligomers: A molecular dynamics study

, Article Physics of Fluids ; Volume 33, Issue 5 , 2021 ; 10706631 (ISSN) Saleki, O ; Moosavi, A ; Hannani, S. K ; Sharif University of Technology

American Institute of Physics Inc 2021

Abstract

Superhydrophobic surfaces have been used for reducing friction in micro- and nanochannels. In the present work, water flow between two carbon walls with nanostructures made of poly(N-isopropylacrylamide) via the molecular dynamics method has been studied. The structure of this polymer can change based on the temperature of the environment, so that by increasing the temperature the structure becomes hydrophobic. This property has been studied and the effect of multiple factors on the slip length is presented. The effects of the number of monomers in the polymer, the distance between the polymers, and the temperature on the flow field are investigated. The results reveal that the slip length...

Friction reduction in grafted carbon nanochannels by applying an electric field

, Article Computational Materials Science ; Volume 213 , 2022 ; 09270256 (ISSN) Saleki, O ; Moosavi, A ; Hannani, S. K ; Sharif University of Technology

Elsevier B.V 2022

Abstract

Water can be pumped in nanochannels by limiting it between the surfaces with different hydrophobicities and exerting a spinning electric field. The asymmetrical hydrophobicity combined with the spinning electric field and the fact that the water molecules have a dipole moment create a situation in which the angular momentum of water molecules is transformed into a linear momentum and the water is pumped into the nanochannel. The hydrophobicity of the surfaces can be manipulated by using nanostructures to reduce friction. In this study, two types of nanostructures have been used which are hierarchical nanostructures and polymer nanostructures made of Poly(N-isopropylacrylamide). The walls of...

Numerical study on the oscillation of a transient bubble near a confined free surface for droplet generation

, Article Theoretical and Computational Fluid Dynamics ; Vol. 28, issue. 4 , 2014 , p. 449-472 Saleki-Haselghoubi, N ; Shervani-Tabar, M.T ; Taeibi-Rahni, M ; Dadvand, A ; Sharif University of Technology

2014

Abstract

In the present work, the oscillation of a spark-created bubble near a confined water-air interface and the ensuing droplet generation and ejection are studied numerically using the boundary element method. The interface is accorded by the top opening of either one of the following symmetrical configurations, which are distinguished by the value of angle between their vertical symmetry axis and lateral wall (i.e., θ): (i) a centrally perforated horizontal flat plate (θ = 90°) and (ii) vertically placed cylinder (θ = 0°), nozzle (θ > 0°) and diffuser (θ < 0°). Furthermore, the influences of the effective parameters such as the strength parameter (i.e., the intensity of local energy input), the...

Molecular Dynamic Simulation of Friction Reduction in Two-Phase Flows with Nanostructures and Study of the effect of Electric Field

, M.Sc. Thesis Sharif University of Technology Saleki, Omid (Author) ; Kazemzadeh Hannani, Siamak (Supervisor) ; Moosavi, Ali (Supervisor)

Abstract

The use of superhydrophobic surfaces is one the most promising methods for reducing the friction and increasing the flow rate in fluid transfer systems. Since in such systems the surface structure plays a key role, in the first part of this study, the performance of the hierarchical nanostructures is explored. These nanostructures are inspired by the superhydrophobic surface of the lotus leaf. The flow is considered between two walls with hierarchical nanostructures and simulate the system via the molecular dynamics (MD) method. The size of the nanostructures and the distance between them have been studied to find whether a design with maximum flow rate exists. The nanostructures have two...

Interaction of two spark-generated bubbles near a confined free surface

, Article Theoretical and Computational Fluid Dynamics ; Volume 30, Issue 3 , 2016 , Pages 185-209 ; 09354964 (ISSN) Saleki Haselghoubi, N ; Shervani Tabar, M. T ; Taeibi Rahni, M ; Dadvand, A ; Sharif University of Technology

Springer New York LLC 2016

Abstract

In this paper, the oscillation of two spark-generated bubbles placed on a vertical column in close proximity to a confined free surface is considered. The confined free surface is accorded by the top opening of different configurations. These configurations include (i) a centrally perforated horizontal flat plate (θ = 90∘), (ii) vertically placed cylinder (θ = 0∘) and (iii) nozzle (θ > 0∘). The main objective of the present work is to study the effects of key parameters such as the nozzle geometry, the locations of the energy input (i.e., initial position of the bubbles with respect to each other and relative to the free surface) on the dynamics of the two bubbles and the free surface. It...

Simulating dynamic plastic continuous neural networks by finite elements

, Article IEEE Transactions on Neural Networks and Learning Systems ; Volume 25, Issue 8 , August , 2014 , Pages 1583-1587 ; ISSN: 2162237X Joghataie, A ; Torghabehi, O. O ; Sharif University of Technology

2014

Abstract

We introduce dynamic plastic continuous neural network (DPCNN), which is comprised of neurons distributed in a nonlinear plastic medium where wire-like connections of neural networks are replaced with the continuous medium. We use finite element method to model the dynamic phenomenon of information processing within the DPCNNs. During the training, instead of weights, the properties of the continuous material at its different locations and some properties of neurons are modified. Input and output can be vectors and/or continuous functions over lines and/or areas. Delay and feedback from neurons to themselves and from outputs occur in the DPCNNs. We model a simple form of the DPCNN where the...

A Deep Learning Approach for Detecting Covid-19 Using the Chest X-Ray Images

, Article Computers, Materials and Continua ; Volume 74, Issue 1 , 2023 , Pages 751-768 ; 15462218 (ISSN) Sadeghi, F ; Rostami, O ; Yi, M. K ; Hwang, S. O ; Sharif University of Technology

Tech Science Press 2023

Abstract

Real-time detection of Covid-19 has definitely been the most widely-used world-wide classification problem since the start of the pandemic from 2020 until now. In the meantime, airspace opacities spreads related to lung have been of the most challenging problems in this area. A common approach to do on that score has been using chest X-ray images to better diagnose positive Covid-19 cases. Similar to most other classification problems, machine learning-based approaches have been the first/most-used candidates in this application. Many schemes based on machine/deep learning have been proposed in recent years though increasing the performance and accuracy of the system has still remained an...

Vertically aligned ZnO@CdS nanorod heterostructures for visible light photoinactivation of bacteria

, Article Journal of Alloys and Compounds ; Vol. 590 , 2014 , pp. 507-513 ; ISSN: 09258388 Zirak, M ; Akhavan, O ; Moradlou, O ; Nien, Y. T ; Moshfegh, A. Z ; Sharif University of Technology

2014

Abstract

Vertically aligned ZnO@CdS nanorod heterostructure films with various loadings of CdS nanoparticle shell were synthesized and applied in photoinactivation of Escherichia coli bacteria under visible light irradiation. While neither the bare ZnO nanorods (with band-gap energy (Eg) of ∼3.28 eV) under visible light irradiation nor the nanorod heterostructures in dark exhibited any significant antibacterial activity, the ZnO@CdS nanorod heterostructures (with Eg ∼2.5-2.6 eV) could successfully inactivate the bacteria under visible light irradiation. Furthermore, it was found that an optimum loading of the CdS shell (corresponding to the effective thickness less than ∼15 nm) is required to achieve...

Metallurgical and mechanical properties of underwater friction stir welds of Al7075 aluminum alloy

, Article Journal of Materials Processing Technology ; Volume 262 , 2018 , Pages 239-256 ; 09240136 (ISSN) Rouzbehani, R ; Kokabi, A. H ; Sabet, H ; Paidar, M ; Ojo, O. O ; Sharif University of Technology

Elsevier Ltd 2018

Abstract

Travel speeds between 25–300 mm/min and tool rotational speeds of 800 and 1250 rpm were employed for this study. The microstructure, mechanical properties and fracture surfaces of the joints were studied. Underwater environment and an increase in travel speed significantly increase the precipitates’ volume fraction, reduce the average grain and precipitate sizes of the weld nugget zones. A critical travel speed of 150 mm/min is attained in underwater welds beyond which the average grain sizes remain relatively the same. Average grain and precipitate sizes have linear relationships with the tool rotational and travel speed ratio. Optimum weld strengths of 396 and 360 MPa were obtained in the...

Pre-threaded hole friction stir spot welding of AA2219/PP-C30S sheets

, Article Journal of Materials Processing Technology ; Volume 273 , 2019 ; 09240136 (ISSN) Paidar, M ; Ojo, O. O ; Moghanian, A ; Karami Pabandi, H ; Elsa, M ; Sharif University of Technology

Elsevier Ltd 2019

Abstract

This paper examines the use of pre-fabricated interlocking arms/threading in enhancing the strength of friction stir spot welded hybrid joints of AA2219/PP-C30S polypropylene polymer by varying parameter combination. The process involves the fabrication of a pre-threaded hole on the Al alloy prior to the joining process, and the threading/crest-pitch profile aids mechanical interlocking. The peak temperature, crest-pitch interlocked profiles, microstructural and mechanical properties of the joints were examined. The results show that an increase in the tool rotational speed increases the thickness of the reaction layer (between the Al and the polymer substrates), the shear-tensile load...

Flexible bactericidal graphene oxide–chitosan layers for stem cell proliferation [electronic resource]

, Article Journal of Applied Surface Science ; 15 May 2014, Volume 301, Pages 456–462 Mazaheri, M ; Akhavan, O ; Simchi, A. (Abdolreza) ; Sharif University of Technology

Abstract

Graphene oxide (GO)–chitosan composite layers with stacked layer structures were synthesized using chemically exfoliated GO sheets (with lateral dimensions of ∼1 μm and thickness of ∼1 nm), and applied as antibacterial and flexible nanostructured templates for stem cell proliferation. By increasing the GO content from zero to 6 wt%, the strength and elastic modulus of the layers increased ∼80% and 45%, respectively. Similar to the chitosan layer, the GO–chitosan composite layers showed significant antibacterial activity (>77% inactivation after only 3 h) against Staphylococcus aureus bacteria. Surface density of the actin cytoskeleton fibers of human mesenchymal stem cells (hMSCs) cultured...

Superparamagnetic zinc ferrite spinel-graphene nanostructures for fast wastewater purification

, Article Carbon ; Vol. 69 , April , 2014 , pp. 230-238 ; ISSN: 00086223 Meidanchi, A ; Akhavan, O ; Sharif University of Technology

2014

Abstract

Superparamagnetic ZnFe2O4/reduced graphene oxide (rGO) composites containing ZnFe2O4 nanoparticles (with ∼5-20 nm sizes) attached onto rGO sheets (with ∼1 μm lateral dimensions) were synthesized by hydrothermal reaction method. By increasing the graphene content of the composite from 0 to 40 wt%, the size as well as the number of the ZnFe2O4 nanoparticles decreased and the saturated magnetization of the composites reduced from 10.2 to 1.8 emu/g, resulting in lower responses to external magnetic fields. Concerning this, the time needed for 90% separation of ZnFe2O4/rGO (40 wt%) composite from its solution (2 mg/mL in ethanol) was found 60 min in the presence of an external magnetic field (∼1...

Visible light-induced photocatalytic reduction of graphene oxide by tungsten oxide thin films

, Article Applied Surface Science ; Volume 276 , 2013 , Pages 628-634 ; 01694332 (ISSN) Choobtashani, M ; Akhavan, O ; Sharif University of Technology

2013

Abstract

Tungsten oxide thin films (deposited by thermal evaporation or sol gel method) were used for photocatalytic reduction of graphene oxide (GO) platelets (synthesized through a chemical exfoliation method) on surface of the films under UV or visible light of the environment, in the absence of any aqueous ambient at room temperature. Atomic force microscopy (AFM) technique was employed to characterize surface morphology of the GO sheets and the tungsten oxide films. Moreover, using X-ray photoelectron spectroscopy (XPS), chemical state of the tungsten oxide films and the photocatalytic reduction of the GO platelets were quantitatively investigated. The better performance of the sol-gel tungsten...

Ethylbenzene dehydrogenation to styrene over fresh and used commercial catalysts

, Article AIChE Annual Meeting, Conference Proceedings ; 2011 ; 9780816910670 (ISBN) Baghalha, M ; Ebrahimpour, O ; Sharif University of Technology

2011

Abstract

Dehydrogenation of ethylbenzene (EB) to produce styrene (ST) monomer is commercially performed over potassium-promoted iron oxide catalysts. Catalyst deactivation due to coke deposition and loss of potassium is a major operation and economic drawback in this process. To better evaluate the performance change of these catalysts over their life-cycle, dehydrogenation of EB to ST over the fresh and used commercial catalysts was experimentally investigated at temperatures from 590 to 639°C under atmospheric pressure. The fresh and the used catalysts were obtained from a styrene plant. The used catalyst had been continuously operated for two years under severe plant conditions. The catalyst...

Improving the photocatalytic activity of graphene oxide/ZnO nanorod films by UV irradiation

, Article Applied Surface Science ; Volume 371 , 2016 , Pages 592-595 ; 01694332 (ISSN) Rokhsat, E ; Akhavan, O ; Sharif University of Technology

Elsevier 2016

Abstract

Graphene oxide (GO) sheets with a low concentration (∼1 wt%) were deposited on surface of hydrothermally synthesized ZnO nanorod films. The deposited films were heat treated at 450 °C in order to achieve suitable GO/ZnO hybrid thin films for photocatalytic purposes. The photocatalytic activity of the nanocomposite films was investigated based on degradation of methylene blue (MB) dye which is a typical pollutant model. The GO/ZnO hybrid thin films could degrade higher MB (∼90%) than the bare ZnO nanorods (which showed only ∼75% degradation) after 450 min UV irradiation. A further significant improvement (resulting in a nearly complete degradation of MB) was achieved by exposing the GO/ZnO...